Gas separation composite membrane and method of producing the same, and gas separating module, gas separation apparatus and gas separation method using the same

ABSTRACT

A gas separation composite membrane, containing a gas-permeable supporting layer and a gas separating layer containing a crosslinked polyimide resin over the gas-permeable supporting layer, in which the crosslinked polyimide resin is formed by a polyimide compound being crosslinked by a radically crosslinkable functional group thereof, and a ratio [η] of a crosslinked site to an imide group of the polyimide compound (the number of crosslinked sites/the number of imide groups) in the crosslinked polyimide resin is 0.0001 or more and 0.45 or less; a method of producing the same; and a gas separating module, a gas separation apparatus and a gas separation method using the same.

TECHNICAL FIELD

The present invention relates to a gas separation composite membrane anda method of producing the same, and a gas separating module, a gasseparation apparatus and a gas separation method using the same.

BACKGROUND ART

A raw material comprising a polymer compound has characteristic gaspermeability for each raw material. Based on properties thereof, adesired gas component can be separated by allowing selective permeationby means of a membrane constituted of a specific polymer compound. As anindustrial application embodiment of this gas separation membrane, studyhas been conducted for separating and recovering carbon dioxide from alarge-scale carbon dioxide source in a thermal power station, a cementplant, a blast furnace in a steel plant or the like in relation to aglobal warming issue. Then, this membrane separation technique attractsattention as a solution to an environmental issue to allow achievementby relatively small energy. Meanwhile, natural gas or bio gas (gasesgenerated by fermentation and anaerobic digestion of excreta oforganisms, organic fertilizers, biodegradable substances, pollutedwater, garbages, energy crops, and the like) is mainly a mixed gas ofmethane and carbon dioxide. Study has been made so far for a membraneseparation method as a means for removing an impurity such as carbondioxide therein (see Patent Literature 1 and Patent Literature 2).Specifically, study has been made for cellulose or polyimide as a rawmaterial in purification of a natural gas. However, the membrane isplasticized under high pressure conditions and high carbon dioxideconcentration in an actual plant, and a decrease of separationselectivity due to the plasticization has become a problem (seeNon-Patent Literature 1, p. 313-322; and Non-Patent Literatures 2 and3). In order to suppress plasticization of the membrane, introduction ofcrosslinked structure into a polymer compound constituting the membraneis known to be effective, and research has been continued forimprovement in a polyimide membrane (see Non-Patent Literature 1, p.3-27). Specific examples of arts utilizing a membrane having acrosslinked structure for the gas separation membrane include artsdescribed in Patent Literature 3, and Non-Patent Literatures 4, 5 and 6.

CITATION LIST Patent Literatures

-   Patent Literature 1: JP-A-2007-297605 (“JP-A” means unexamined    published Japanese patent application)-   Patent Literature 2: JP-A-2006-297335-   Patent Literature 3: U.S. Pat. No. 7,247,191

Non-Patent Literatures

-   Non-Patent Literature 1: Yuri Yampolskii, Benny Freeman, Membrane    Gas Separation, 2010, Johns Wiley & Sons Ltd.-   Non-Patent Literature 2: Industrial & Engineering Chemistry    Research, 2008, 47, 2109-   Non-Patent Literature 3: Industrial & Engineering Chemistry    Research, 2002, 41, 1393-   Non-Patent Literature 4: Journal of Membrane Science, 1999, 155, 145-   Non-Patent Literature 5: Journal of Membrane Science, 2000, 175, 181-   Non-Patent Literature 6: European Polymer Journal, 1997, 33, 1717

SUMMARY OF THE INVENTION Technical Problem

Incidentally, in order to constitute a practical gas separationmembrane, high gas permeability should be provided by processing a rawmaterial into a thin layer. An attempt has been made so far forprocessing a single raw layer into an asymmetric membrane, therebyprocessing a part contributing to separation into the thin layerreferred to as a skin layer to satisfy high gas permeability, separationselectivity and also mechanical strength. However, the single rawmaterial is difficult to be processed into one uniting these properties.Therefore, from viewpoints of performance and cost, a composite membraneis desirable in which separate raw materials bear a separation functionand a function for providing the membrane with the mechanical strength,and the composite membrane is becoming mainstream in a reverse osmosismembrane for water treatment.

On the other hand, examples are few in which a crosslinked structuremembrane is utilized for a separating layer in the gas separationmembrane (see Patent Literature 3, and Non-Patent Literatures 4, 5 and6). According to these methods, a high temperature of 100° C. or higheror a very long time is required to crosslinking in some cases.Therefore, these methods have been still insufficient for providing apractical gas separation membrane having excellent membrane-formingcompetence and also high mechanical strength, and excellent durability,while maintaining high gas permeability and separation selectivity.

In view of the above-described respects, the present invention providesa gas separation composite membrane that has excellent gas permeabilityand also realizes high gas separation selectivity and further attainshigh membrane-forming competence; a method of producing the same; and amodule and a gas separation apparatus using the same.

Solution to Problem

In view of the above-described technical problems, the present inventorsconducted study. As a result, the present inventors found that, in orderto provide a gas separation membrane with membrane-forming competencewhile maintaining high gas permeability and separation selectivity inthe gas separation membrane, a composite membrane using a supportinglayer is formed, and then a ratio of primary structure into which acrosslinking functional group is introduced, to a crosslinked site isspecified for a polymer constituting a separating layer, therebyallowing hardening by crosslinking under mild conditions, and thus theabove-described problems can be solved. The present invention was madebased on these findings.

The above-described problems can be solved by the following means.

(1) A gas separation composite membrane, containing:

a gas-permeable supporting layer; and

a gas separating layer containing a crosslinked polyimide resin over thegas-permeable supporting layer,

wherein the crosslinked polyimide resin is formed by a polyimidecompound being crosslinked by a radically crosslinkable functional groupthereof, andwherein a ratio [η] of a crosslinked site to an imide group of thepolyimide compound (the number of crosslinked sites/the number of imidegroups) in the crosslinked polyimide resin is 0.0001 or more and 0.45 orless.(2) The gas separation composite membrane as described in the above item(1), wherein the radically crosslinkable functional group contains anethylenically unsaturated group.(3) The gas separation composite membrane as described in the above item(1) or (2),wherein the radically crosslinkable functional group contains a linkinggroup in which a crosslinked structural site is represented by—C(R^(A1))₂CH₂—; andwherein R^(A1) represents a hydrogen atom, an alkyl group having 1 to 10carbon atoms, R^(A2)—C(═O)O— or —R^(A2)—OC(═O)—, and R^(A2) representsan alkylene having 1 to 10 carbon atoms.(4) The gas separation composite membrane as described in any one of theabove items (1) to (3), wherein the polyimide compound contains arepeating unit represented by Formula (I):

wherein R represents a structure part containing at least onehydrocarbon ring having 5 to 12 carbon atoms.

(5) The gas separation composite membrane as described in any one of theabove items (1) to (4),wherein the polyimide compound further contains at least one kind ofrepeating unit represented by Formula (II-a) or (II-b), and at least onekind of repeating unit represented by Formula (III-a) or (III-b), andwherein R of the repeating unit represented by Formula (I) is a group ofatoms selected from the group consisting of the groups represented byany one of Formulas (I-a) to (I-g):

wherein, in Formulas (I-a) to (I-g), X¹ represents a single bond or abivalent linking group; Y¹ represents a methylene group or a vinylenegroup; R¹ and R² each independently represent a hydrogen atom or asubstituent, or may bond with each other to form a ring; and the symbol“*” represents a binding site with the carbonyl group of the imide inFormula (I);

wherein, in Formulas (II-a) and (II-b), R³ represents an alkyl group, ahydroxyl group, a carboxyl group, a sulfonic acid group, an amino groupor a halogen atom; l1 represents an integer of from 0 to 4; R⁴ and R⁵each independently represent an alkyl group, a hydroxyl group, acarboxyl group, a sulfonic acid group, an amino group or a halogen atom;R⁴ and R⁵ may bond with each other to form a ring; m1 and n1 eachindependently represent an integer of from 0 to 4; and X² represents asingle bond or a bivalent linking group; and

wherein, in Formulas (III-a) and (III-b), R⁶, R⁷ and R⁸ eachindependently represent a substituent; R⁷ and R⁸ may bond with eachother to form a ring; J¹, J² and W¹ each independently represent asingle bond or a bivalent linking group; l2, m2 and n2 eachindependently represent an integer of from 0 to 3; L¹ represents abivalent linking group; L² represents a functional group; p representsan integer of 0 or more; when p is 2 or more, L¹'s and J²'s may be thesame or different from each other; and X³ represents a single bond or abivalent linking group.

(6) The gas separation composite membrane as described in any one of theabove items (1) to (5), wherein a ratio [γ] of the functional group L²of the repeating unit represented by Formula (III-a) or (III-b) to therepeating unit represented by Formula (I) (the number of functionalgroup L²'s/the number of repeating units represented by Formula (I)) isfrom 0.003 to 0.68.(7) The gas separation composite membrane as described in any one of theabove items (1) to (6), wherein the supporting layer contains a porouslayer on a side of the gas separating layer and a nonwoven fabric layeron a side reverse thereto.(8) The gas separation composite membrane as described in the above item(7), wherein the porous layer has a molecular weight cut-off of 100,000or less.(9) The gas separation composite membrane as described in any one of theabove items (1) to (8),wherein a gas to be supplied is a mixed gas of carbon dioxide andmethane,wherein a transmission rate of the carbon dioxide at 40° C. and 8atmospheric pressure is more than 20 CPU, andwherein a ratio of the transmission rate of the carbon dioxide to atransmission rate of the methane (TR_(CO2)/TR_(CH4)) is 20 or more.(10) A method of producing a gas separation composite membrane,wherein the gas separation composite membrane contains a gas-permeablesupporting layer, and a gas separating layer containing a crosslinkedpolyimide resin over the gas-permeable supporting layer,wherein the method contains the steps of:

coating a coating liquid containing a polyimide compound having aradically crosslinkable functional group over the supporting layer, and

allowing reaction of the crosslinkable functional group by irradiatingthe coating liquid with active radiation or providing the coating liquidwith heat to crosslink the polyimide compound, and

wherein a ratio [η] of a crosslinked site to an imide group of thepolyimide compound (the number of crosslinked sites/the number of imidegroups) is adjusted to be 0.0001 or more and 0.45 or less.(11) A method of producing a gas separation composite membrane,wherein the gas separation composite membrane contains a gas-permeablesupporting layer, and a gas separating layer containing a crosslinkedpolyimide resin over the gas-permeable supporting layer,wherein the method contains the steps of:

coating a coating liquid containing a polyimide compound having aradically crosslinkable functional group over the supporting layer, and

allowing reaction of the crosslinkable functional group by irradiatingthe coating liquid with active radiation or providing the coating liquidwith heat to crosslink the polyimide compound, and

wherein a crosslinking conversion ratio [α] is adjusted to be 20% ormore and 100% or less.(12) A gas separation module, containing the gas separation compositemembrane as described in any one of the above items (1) to (9).(13) A gas separation apparatus, containing the gas separation module asdescribed in the above item (12).(14) A gas separation method, which contains a step of selectivelypermeating carbon dioxide from a gas containing carbon dioxide andmethane by using the gas separation composite membrane as described inany one of the above items (1) to (9).

When a plurality of substituents, linking groups or the like(hereinafter, referred to as “substituent or the like”) represented by aspecific symbol are described herein, or a plurality of substituents orthe like are simultaneously or alternatively defined herein, respectivesubstituents or the like may be identical or different. This is appliedto a definition of the number of substituents or the like in a similarmanner. Moreover, unless otherwise noted, when a plurality ofsubstituents or the like are close, they may be linked with each otheror subjected to ring condensation, thereby forming a ring.

Moreover, when an expression “may bond with each other to form a ring”is referred to herein, the expression may include ones that are bondedby a single bond, a double bond or the like to form cyclic structure, orones that are subjected to ring condensation to form condensed ringstructure.

In the present specification, when the name of a chemical is called byputting the term “compound” at the foot of the chemical name, or whenthe chemical is shown by a specific name or a chemical formula, ashowing of the compound is used to mean not only the compound itself,but also a salt, a complex or ion thereof and the like. Further, theshowing of the compound is also used to mean incorporation ofderivatives having a predefined substituent or modified by a predefinedconfiguration to an extent necessary to obtain a desired effect.Further, in the present specification, when a specific group of atoms ora specific compound is called by putting the term “group” at the foot ofthe specific group of atoms or the specific compound with respect to thesubstituent, the group means that the group of atoms or the compound mayhave further an arbitrary substituent.

Advantageous Effects of Invention

The gas separation composite membrane according to the present inventionhas excellent gas permeability and also realizes high gas separationselectivity and further attains high membrane-forming competence.Moreover, the present invention allows provision of a high-performancegas separating module, gas separation apparatus and gas separationmethod using the same. Further, a method of producing a gas separationcomposite membrane according to the present invention allows productionof a gas separation composite membrane that develops the above-describedhigh performance.

Other and further features and advantages of the invention will appearmore fully from the following description, appropriately referring tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross section schematically illustrating one embodiment ofthe gas separation composite membrane according to the presentinvention.

FIG. 2 is a cross section schematically illustrating another embodimentof the gas separation composite membrane according to the presentinvention.

MODE FOR CARRYING OUT THE INVENTION

The gas separation composite membrane according to the present inventionhas a gas separating layer containing a crosslinked polyimide resin overa gas-permeable supporting layer. Then, the-above described crosslinkedpolyimide resin is formed by a polyimide compound being crosslinked by aradically crosslinkable functional group, and a ratio [η] of crosslinkedsites to the imide groups (the number of crosslinked sites/the number ofimide groups) (hereinafter, referred to as “crosslinked site ratio”) isadjusted in a specific range. Thus, crosslinking is performed by theradically crosslinkable functional group, and the specific crosslinkedsite ratio is satisfied, thereby producing an excellent effect on gasseparation. This reason (mechanism of action) includes points yet to bedefined, but is estimated as described below.

First, when a gas separating mechanism by a membrane is examined, when agas molecule permeates a thin film, consideration is made to a role of aKnudsen mechanism or a Hagen-Poiseuille mechanism (porous membrane), asurface diffusion mechanism (porous membrane), a molecular sievemechanism (porous membrane), a dissolution and diffusion mechanism(nonporous membrane) or the like (see “Shintei Saishin Polyimide-Kiso toOyo-,” 365 to 376, edited by Nihon Polyimide Hokozokukei KobunshiKenkyukai). Here, when separation of CO₂ and CH₄ is referred to, bothare a low-molecular-weight compound, and molecular sizes to be separatedare approximated. In such a case, control of the above-describeddissolution and diffusion mechanism becomes important (see“Kitaibunrimaku, Tokamaku, Bariamaku no Saishingijyutsu,” pp. 52-59,compiled under the supervision by Kazukiyo Nagai, CMC Publishing CO.,LTD.). Therefore, in order to selectively improve permeability(permeability coefficient) of carbon dioxide to a gas to be separated, asolubility coefficient (solubility) and/or a diffusion coefficient(diffusibility) of carbon dioxide to a polymer membrane only needs to beselectively improved. Carbon dioxide has quadrupolar structure polarizedin a molecule, and has affinity with chemical structure having polarity.For example, polyethylene glycol is reported to have high solubilitywith carbon dioxide (see Journal of Physical Chemistry, 1990, 94,2124-2128). Study has been made for a separation membrane containing apolyethyleneoxy (PEO) composition by taking an advantage of such aviewpoint (see Journal of Membrane Science, 1999, 160, 87-99,JP-A-7-60079, WO 08/143,514, WO 08/143,515, and WO 08/143,516). Thisresults from strong interaction of carbon dioxide with thepolyethyleneoxy composition. This polyethyleneoxy membrane is a flexibleand rubbery polymer membrane having a low glass transition temperature,and therefore a difference of diffusion coefficients depending on gasspecies is small, and separation selectivity is mainly caused due to aneffect of a difference in solubility.

In contrast, according to the present invention, the crosslinked siteratio [η] is set to be somewhat low in a suitable range in crosslinkedpolyimide having a high glass transition temperature. Therefore, a gapthrough which a molecule is permeated is secured (high gaspermeability). On the one hand, a polymer chain of polyimide is linkedby a specific radically crosslinkable functional group. Therefore,characteristic diffusion selectivity (high gas selectivity) isconsidered to be developed by a crosslinked form thereof being optimizedin combination with solubility and diffusibility of the polyimidecompound. Moreover, a uniform and degradation-free crosslinked form isrealized by being subjected to radical crosslinking, which is consideredto have good bending properties and to be adapted for a thin supportinglayer and to develop excellent production competence. Hereinafter, thepresent invention is described in detail.

[Composite Membrane]

The composite membrane according to the present invention has a gasseparating layer containing a crosslinked polyimide resin formed over agas-permeable supporting layer. This composite membrane is preferablyformed by coating a coating liquid (dope) to form the above-describedgas separating layer (“coating” herein includes an embodiment in whichthe coating liquid is attached on the surface by dipping) at least on asurface of a porous support, and irradiating the resultant coatedsurface with active radiation. FIG. 1 is a cross-sectional viewschematically showing a gas separation composite membrane 10, being apreferred embodiment according to the present invention. The referencesign 1 is a gas separating layer and the reference sign 2 is asupporting layer constituted of a porous layer. FIG. 2 is across-sectional view schematically showing a gas separation compositemembrane 20, being a preferred embodiment according to the presentinvention. According to this embodiment, in addition to the gasseparating layer 1 and the porous layer 2, a nonwoven fabric layer 3 isadded as the supporting layer.

An expression “over the supporting layer” means that any other layer maybe interposed between the supporting layer and the gas separating layer.In addition, unless otherwise noted, with regard to expressions “over”and “under”, a direction in which a gas to be separated is supplied isreferred to as “over”, and a direction from which a separated gas isdischarged is referred to “under”.

The gas separation composite membrane according to the present inventionmay have the gas separating layer formed and arranged on the surface orinside of the porous support (supporting layer). The gas separatinglayer is formed at least on the surface, and thus the composite membranecan be simply realized. Formation of the gas separating layer at leaston the surface of the porous support allows realization of a compositemembrane having advantages of high separation selectivity, high gaspermeability and also mechanical strength. Regarding the membranethickness of the separating layer, the membrane is preferably as thin aspossible under conditions to provide superior gas permeability whilemaintaining mechanical strength and separation selectivity.

The thickness of the gas separating layer of the gas separationcomposite membrane according to the present invention is notparticularly limited, but is preferably from 0.01 to 5.0 μm, and morepreferably from 0.1 to 2.0 μm. Herein, a term “to” is used in themeaning of being identical with a symbol “-”, and includes numericalvalues or numbers defined before and after the values.

The porous support (porous layer) preferably applied for the supportlayer is not particularly limited so long as it satisfies mechanicalstrength and high gas permeability, may be a porous membrane made of anyorganic or inorganic substance and is preferably an organic polymerporous membrane. The thickness thereof is preferably from 1 to 3,000 μm,more preferably from 5 to 500 μm, and further preferably from 5 to 150μm. Regarding this fine pore structure of porous membrane, a mean porediameter is ordinarily 10 μm or less, preferably 0.5 μm or less, andmore preferably 0.2 μm or less, and a porosity is preferably from 20% to90%, and more preferably from 30% to 80%. In addition, the gaspermeability is preferably 3×10⁻⁵ cm³(STP)/cm²·sec·cmHg (30 GPU) ormore, based on carbon dioxide permeation rate.

Herein, 1 GPU is defined to be 1×10⁻⁶ cm³ (STP)/cm²·sec·cmHg.

Examples of the material for the porous membrane include conventionallyknown polymers, including polyolefin-based resins such as polyethyleneand polypropylene; fluorine-containing resins such aspolytetrafluoroethylene, polyvinyl fluoride, and polyvinylidenefluoride; and various resins such as polystyrene, cellulose acetate,polyurethane, polyacrylonitrile, polyphenyleneoxide, polysulfone,polyethersulfone, polyimide and polyaramide. Above all, from viewpointsof excellent production competence upon coating the above-describedpolyimide compound and performing crosslinking, attaining both of highgas permeability and separation selectivity, the supporting layer ispreferably constituted of polyacrylonitrile, polysulfone orpolyphenylene oxide, and further preferably polyacrylonitrile. The shapeof the porous membrane may be any of plate, spiral, tubular or hollowfibers.

In the present invention, application of the supporting layer formingthe gas separating layer is to be essentially required. As mentionedabove, this supporting layer being a thin and porous raw material ispreferred due to capability of securing sufficient gas permeability.Moreover, the supporting layer is preferably in a thin membrane andporous form also for maximizing excellent gas separation selectivity ofthe gas separating layer as mentioned later. On the one hand, whensevere reaction conditions such as a high temperature and long time areimposed on shaping of the gas separation membrane, the conditions mayoccasionally damage the above-mentioned thin and porous supporting layernot to allow development of sufficient performance as the compositemembrane. From such a viewpoint, the gas separation composite membraneusing the radically crosslinkable polyimide compound employed in thepresent invention can be formed under mild conditions, produce anexcellent effect, and develop high performance in both of productioncompetence and product quality.

In the present invention, in order to further provide the membrane withmechanical strength, a support is desirably formed in a lower part (on aside opposite to the gas separating layer) of the porous layer being thesupporting layer for forming the gas separating layer. Specific examplesof such a support include a woven fabric, a nonwoven fabric and a net,and a nonwoven fabric is preferably used in view of membrane-formingproperties and cost. As the nonwoven fabric, fibers formed of polyester,polypropylene, polyacrylonitrile, polyethylene, polyamide or the likemay be used alone or in combination with a plurality of fibers. Thenonwoven fabric can be produced, for example, by paper making of mainfibers and binder fibers that are uniformly dispersed in water, using acylinder mold, a fourdrinier or the like, and drying the resultantproduct by a drier. Moreover, the nonwoven fabric is preferablyinterposed between two rolls and subjected to pressure heatingprocessing for the purpose of removing fluff or improving mechanicalproperties.

In the present invention, a cutoff molecular weight of the porous layeris preferably 100,000 or less.

The gas separating composite membrane according to the present inventioncan be preferably used for a gas separation recovery method or a gasseparation purification method. For example, the gas separatingcomposite membrane can be processed into a gas separation membrane thatcan efficiently separate a specific gas from a gaseous mixturecontaining hydrogen, helium, carbon monoxide, carbon dioxide, hydrogensulfide, oxygen, nitrogen, ammonia, sulfur oxide, nitrogen oxide, ahydrocarbon such as methane and ethane, an unsaturated hydrocarbon suchas propylene, or a gas of a perfluoro compound, such astetrafluoroethane. In particular, the gas separating composite membraneis preferably processed into a gas separation membrane for selectivelyseparating carbon dioxide from a gaseous mixture containing carbondioxide/hydrocarbon (methane), and is preferably applied to the methodof producing the same, and is preferably assembled into a module or aseparation apparatus using the same.

Above all, a gas to be supplied is preferably a mixed gas of carbondioxide and methane, a transmission rate of carbon dioxide at 40° C. and8 atmospheric pressure is preferably more than 20 GPU, more preferablyfrom 20 to 300 GPU. A ratio of transmission rates (TR_(CO2)/TR_(CH4)) ofcarbon dioxide and methane is preferably 20 or more, more preferablyfrom 20 to 50.

To the above-described selective gas permeation, consideration is madeto the role of the dissolution and diffusion mechanism to the membraneas mentioned above. Study has been made for a separation membranecontaining a polyethyleneoxy (PEO) composition by taking an advantage ofsuch a viewpoint (see Journal of Membrane Science, 1999, 160, 87-99).This results from strong interaction of carbon dioxide with thepolyethyleneoxy composition. This polyethyleneoxy membrane is a flexibleand rubbery polymer membrane having a low glass transition temperature,and therefore a difference of diffusion coefficients depending on gasspecies is small, and separation selectivity is mainly caused due to aneffect of a difference in solubility. On the other hand, according tothe present invention, a glass transition temperature of the polyimidecompound used for gas separation is high, and while the above-describeddissolution and diffusion action is developed, thermal durability of themembrane can also be significantly improved.

[Polyimide Compound] (Radically Crosslinkable Functional Group)

The polyimide compound forming the crosslinked polyimide resin that isapplied to the gas separating layer according to the present inventionis not particularly limited, but has a radically crosslinkablefunctional group. This radically crosslinkable functional group is notparticularly limited, but is preferably an ethylenically unsaturatedgroup.

The ethylenically unsaturated group includes a group having acarbon-to-carbon double bond that is not a double bond in an aromaticring. The ethylenically unsaturated group preferably includes a groupincluding —CR═CH₂. Here, R represents a hydrogen atom or an alkyl grouphaving 1 to 4 carbon atoms. R is preferably a hydrogen atom or a methylgroup.

Specific examples of the ethylenically unsaturated group include a vinylgroup (—CH═CH₂), an allyl group (—CH₂—CH═CH₂), a vinyl aryl group(—Ar—CH═CH₂, wherein Ar represents a substituted or unsubstitutedaromatic group) and a (meth)acryloyl group (—C(═O)CR═CH), wherein R isdefined in a manner identical with the above-described definitions).Specific examples of a group having a (meth)acryloyl group include a(meth)acryloyloxy group (—O—C(═O)CR═CH₂) and a (meth)acryloylamino group(—N(R′)—C(═O)CR═CH₂, wherein R′ represents a hydrogen atom or an alkylgroup having 1 to 10 carbon atoms).

The polyimide compound preferably has the radically crosslinkablefunctional group on a side chain of the polyimide compound, and may havethe group in a tetracarboxylic acid component or a diamine component ofthe polyimide compound.

In the present invention, the polyimide compound preferably has theradically crosslinkable functional group in the diamine component.

The polyimide compound for use in the present invention is formed of atetracarboxylic acid component and a diamine compound component, but anykind of the tetracarboxylic acid component and the diamine compoundcomponent may be allowed.

The tetracarboxylic acid of the tetracarboxylic acid component and thediamine compound of the diamine compound component may be an aromatic oraliphatic tetracarboxylic acid or diamine compound or may have aheterocyclic ring (an aromatic heterocyclic ring or non-aromaticheterocyclic ring).

In the present invention, the tetracarboxylic acid component and thediamine compound each are preferably an aromatic one.

The polyimide compound for use in the present invention preferablycontains a repeating unit represented by Formula (I).

In Formula (I), R represents a structure part containing at least onehydrocarbon ring having 5 to 12 carbon atoms.

R is preferably a group of atoms selected from the group consisting ofthe groups represented by any one of Formulas (I-a) to (I-g).

In Formulas (I-a) to (I-g), X¹ represents a single bond or a bivalentlinking group. Y¹ represents a methylene group or a vinylene group. R¹and R² each independently represent a hydrogen atom or a substituent.Alternatively, R¹ and R² may bond with each other to form a ring. Thesymbol “*” represents a binding site with the carbonyl group of theimide in Formula (I).

It is further preferable that the polyimide compound further contains atleast one kind of repeating unit represented by Formula (II-a) or (II-b)and at least one kind of repeating unit represented by Formula (III-a)or (III-b), and R of the repeating unit represented by Formula (I) is agroup of atoms selected from the group consisting of the groupsrepresented by any one of Formulas (I-a) to (I-g).

In Formulas (II-a) and (II-b), R³ represents an alkyl group, a hydroxylgroup, a carboxyl group, a sulfonic acid group, an amino group or ahalogen atom. l1 represents an integer of from 0 to 4. R⁴ and R⁵ eachindependently represent an alkyl group, a hydroxyl group, a carboxylgroup, a sulfonic acid group, an amino group or a halogen atom. R⁴ andR⁵ may bond with each other to form a ring. m1 and n1 each independentlyrepresent an integer of from 0 to 4. X² represents a single bond or abivalent linking group.

Herein, the “amino group” includes an amino group, an alkylamino group,an arylamino group and a heterocyclic amino group.

In Formulas (III-a) and (III-b), R⁶, R⁷ and R⁸ each independentlyrepresent a substituent. R⁷ and R⁸ may bond with each other to form aring. J¹, J² and W¹ each independently represent a single bond or abivalent linking group. l2, m2 and n2 each independently represent aninteger of from 0 to 3. L¹ represents a bivalent linking group. L²represents a functional group. p represents an integer of 0 or more.When p is 2 or more, L¹'s and J²'s may be the same or different fromeach other. X³ represents a bivalent linking group.

Among Formulas (II-a) and (II-b), the repeating unit represented byFormula (II-a) is preferred in the present invention. Even in therepeating unit represented by Formula (II-a), the repeating unitpreferably has two bonding hands constituting a polymer main chain atthe para position or the meta position with each other. With regard toone at the para position, a subscript l1 is preferably 3 to 4. Withregard to one at the meta position, l1 is preferably from 0 to 2, morepreferably 0 or 2, and most preferably 0.

In the repeating unit represented by Formula (II-a), the repeating unitpreferably has at least two kinds of repeating units having differentstructure. Among the units, a combination of the above-described onelinked at the para position and the above-described one linked at themeta position is preferred.

Among Formulas (III-a) and (III-b), the repeating unit represented byFormula (III-a) is preferred in the present invention.

Among the repeating unit represented by Formula (III-a), the repeatingunit represented by Formula (III-a1) is further preferred.

In Formula (III-a1), R⁶, l², J¹, W¹, L¹, J², L² and p have the samemeaning as those in Formula (III-a), respectively, and preferable rangesare also the same.

R in Formula (I) may be occasionally referred to as a scaffold. Thisscaffold (R) is preferably represented by Formula (I-a), (I-b) or (I-c),more preferably Formula (I-a) or (I-c), and particularly preferablyFormula (I-a).

X¹, X² and X³

X¹, X² and X³ are contained in Formulas (1-a), (II-b) and (III-b). X¹,X² and X³ each independently represent a single bond or a divalentlinking group. Specifically, X¹, X² and X³ each are preferably a singlebond, —C(Ra)₂- (Ra represents a hydrogen atom or a substituent; and whenRa is a substituent, two Ra's may bond with each other to form a ring),—O—, —SO₂—, —C(═O)—, or —S—; more preferably —C(Ra)₂-, —O—, —SO₂—, or—C(═O)—; and further preferably —C(Ra)₂-. Herein, Ra is preferably ahydrogen atom or an alkyl group, more preferably an alkyl group, andparticularly preferably CF₃.

R¹ and R²

R¹ and R² each independently represent a hydrogen atom or a substituent.As the substituent, any one selected from the below-mentionedsubstituent group Z can be each independently applied. On referring tothe substituent herein, unless otherwise noted, the below-mentionedsubstituent group Z is applied as a preferred range.

R¹ and R² each are preferably a hydrogen atom or an alkyl group; morepreferably a hydrogen atom, a methyl group or an ethyl group; andfurther preferably a hydrogen atom.

R³, R⁴ and R⁵

R³, R⁴ and R⁵ each independently represent an alkyl group, a hydroxylgroup, a carboxyl group, a sulfonic acid group, an amino group or ahalogen atom. These preferred ones are defined in a manner identicalwith the definitions in the substituent group Z. Subscripts l1, m1 andn1 representing the number of substituents described above are aninteger from 0 to 4, preferably from 1 to 4, and more preferably 3 or 4.

R³ is preferably an alkyl group or a halogen atom, more preferably analkyl group, and particularly preferably a methyl group. l1 is mostpreferably 4.

Here, when a plurality of R³, R⁴ and R⁵ are present for each, these maybond with each other to form a ring. Alternatively, R⁴ and R⁵ may bondwith each other to form a ring.

In the present invention, one in which R⁴ and R⁵ bond with each other toform a ring is also preferred, and specific examples of the group formedby linking of R⁴ and R⁵ include —SO₂—, —CH₂—, —O— and —S—.

R⁶, R⁷ and R⁸

R⁶, R⁷ and R⁸ each independently represent a substituent. Thesepreferred ones are defined in a manner identical with the definitions inthe substituent group Z. Subscripts l2, m2 and n2 representing thenumber of substituents described above are an integer from 0 to 3,preferably from 0 to 2, more preferably 0 or 1, and particularlypreferably 0.

Here, when a plurality of R⁶, R⁷ and R⁸ are present for each, these maybond with each other to form a ring. Alternatively, R⁷ and R⁸ may bondwith each other to form a ring.

In the present invention, one in which R⁷ and R⁸ bond with each other toform a ring is also preferred, and specific examples of the group formedby linking of R⁷ and R⁸ include —SO₂—, —CH₂—, —O— and —S—.

J¹ and J²

J¹ and J² each independently represent a single bond or a bivalentlinking group. Specifically, the bivalent linking group is preferably*—O—**, *—S—**, *—C(═O)—**, *—C(═O)O—**, *—C(═O)NR⁹—**, *—OC(═O)—**,*—COO⁻NH⁺(R¹⁰)(R¹¹)—**, *—SO₃ ⁻—NH⁺(R¹²)(R¹³)—**, a methylene group, aphenylene group, or *—C₆H₅C(═O)—**. Herein, R¹⁰ and R¹¹ may bond witheach other to form a ring. In addition, R¹² and R¹³ may bond with eachother to form a ring.

Here, the symbol “*” represents a bonding hand on a side of L¹ for J² oron a side of the phenylene group for J¹, and the symbol “**” representsa bonding hand reverse thereto. R⁹, R¹⁰, R¹¹, R¹² and R¹³ eachindependently represent a hydrogen atom, an alkyl group, an aryl group,or an aralkyl group.

The bivalent linking group of J¹ and J² is more preferably *—C(═O)—**,*—C(═O)O—**, *—C(═O)NR⁹—**, *—OC(═O)—**, a methylene group, a phenylenegroup, or *—C₆H₄C(═O)—**. A preferred range of R⁹ to R¹³ is defined in amanner identical with the definitions of the preferred range of thealkyl group or the aryl group of the substituent group Z.

J¹ and J² each are further preferably *—C(═O)—**, *—C(═O)O—** or*—OC(═O)—**; and particularly preferably *—C(═O)O—**.

W¹

W¹ represents a single bond or a bivalent linking group. Examples of thebivalent linking group include linear, branched or cyclic alkylenegroups (preferably alkylene groups having 1 to 30 carbon atoms, morepreferably alkylene groups having 1 to 12 carbon atoms, furtherpreferably alkylene groups having 1 to 4 carbon atoms, examples thereofinclude methylene, ethylene, propylene, butylene, pentylene, hexylene,octylene, decylene and the like), alkyleneoxy groups (preferablyalkyleneoxy groups having 1 to 30 carbon atoms, more preferablyalkyleneoxy groups having 1 to 12 carbon atoms, further preferablyalkyleneoxy groups having 1 to 4 carbon atoms, and examples thereofinclude methyleneoxy, ethyleneoxy, propyleneoxy, butyleneoxy,pentyleneoxy, hexyleneoxy, octyleneoxy, decyleneoxy and the like),aralkylene groups (preferably aralkylene groups having 7 to 30 carbonatoms, more preferably aralkylene groups having 7 to 13 carbon atoms,and examples thereof include benzylidene, cinnamylidene and the like),arylene groups (preferably arylene groups having 6 to 30 carbon atoms,more preferably arylene groups having 6 to 15 carbon atoms, and examplesthereof include phenylene, cumenylene, mesitylene, tolylene, xylene andthe like) and the like. These may further have a substituent. As afurther substituent, a hydroxy group or a halogen atom is preferred, ahydroxy group or a fluorine atom is more preferred, and a fluorine atomis particularly preferred. In addition, a compound having an ether bondin the molecule is also preferred.

L¹

L¹ represents a bivalent linking group. Specific examples thereofinclude a linking group composed of a repeating unit represented by anyone of (L-1) to (L-35) described below or a combination thereof. Herein,the symbol “*” of the following linking group is a bonding hand on aside of W¹, and the symbol “**” is a bonding hand on a side of J².

L¹ is preferably any one of formulas (L-1) to (L-35), an alkylene group,an alkyleneoxy group or an arylene group; more preferably an alkylenegroup or an alkyleneoxy group; further preferably a group having anether bond in the molecule.

L²

L² represents a functional group. As the functional group, a radicallycrosslinkable functional group is preferred. Above all, the functionalgroup is preferably a (meth)acryloyl group, a (meth)acryloyloxy group, a(meth)acryloylamino group, a vinyl group, an allyl group or a styrylgroup; more preferably a (meth)acryloyl group, a (meth)acryloyloxy groupor a (meth)acryloylamino group; and particularly preferably a(meth)acryloyl group.

p

p represents an integer of 0 or more, preferably an integer of from 0 to10, and more preferably an integer of from 0 to 5. Adjustment of p tothe above-described lower limit or more allows a crosslinking reaction,and adjustment to the above-described upper limit or less allowssuppression of a decrease in permeability.

Substituent Group Z includes:

an alkyl group (preferably an alkyl group having 1 to 30 carbon atoms,more preferably an alkyl group having 1 to 20 carbon atoms, particularlypreferably an alkyl group having 1 to 10 carbon atoms, and examplesthereof include methyl, ethyl, iso-propyl, tert-butyl, n-octyl, n-decyl,and n-hexadecyl), a cycloalkyl group (preferably a cycloalkyl grouphaving 3 to 30 carbon atoms, more preferably a cycloalkyl group having 3to 20 carbon atoms, particularly preferably a cycloalkyl group having 3to 10 carbon atoms, and examples thereof include cyclopropyl,cyclopentyl, cyclohexyl and the like), an alkenyl group (preferably analkenyl group having 2 to 30 carbon atoms, more preferably an alkenylgroup having 2 to 20 carbon atoms, particularly preferably an alkenylgroup having 2 to 10 carbon atoms, and examples thereof include vinyl,allyl, 2-butenyl, 3-pentenyl and the like), an alkynyl group (preferablyan alkynyl group having 2 to 30 carbon atoms, more preferably an alkynylgroup having 2 to 20 carbon atoms, particularly preferably an alkynylgroup having 2 to 10 carbon atoms, and examples thereof includepropargyl, 3-pentynyl and the like), an aryl group (preferably an arylgroup having 6 to 30 carbon atoms, more preferably an aryl group having6 to 20 carbon atoms, particularly preferably an aryl group having 6 to12 carbon atoms, and examples thereof include phenyl, p-methylphenyl,naphthyl, anthranyl and the like), an amino group (including an aminogroup, an alkylamino group, an arylamino group and a heterocyclic aminogroup; preferably an amino group having 0 to 30 carbon atoms, morepreferably an amino group having 0 to 20 carbon atoms, particularlypreferably an amino group having 0 to 10 carbon atoms, and examplesthereof include amino, methylamino, dimethylamino, diethylamino,dibenzylamino, diphenylamino, ditolylamino and the like), an alkoxygroup (preferably an alkoxy group having 1 to 30 carbon atoms, morepreferably an alkoxy group having 1 to 20 carbon atoms, particularlypreferably an alkoxy group having 1 to 10 carbon atoms, and examplesthereof include methoxy, ethoxy, butoxy, 2-ethylhexyloxy and the like),an aryloxy group (preferably an aryloxy group having 6 to 30 carbonatoms, more preferably an aryloxy group having 6 to 20 carbon atoms,particularly preferably an aryloxy group having 6 to 12 carbon atoms,and examples thereof include phenyloxy, 1-naphthyloxy, 2-naphthyloxy andthe like), a heterocyclic oxy group (preferably a heterocyclic oxy grouphaving 1 to 30 carbon atoms, more preferably a heterocyclic oxy grouphaving 1 to 20 carbon atoms, particularly preferably a heterocyclic oxygroup having 1 to 12 carbon atoms, and examples thereof includepyridyloxy, pyrazyloxy, pyrimidyloxy, quinolyloxy and the like),an acyl group (preferably an acyl group having 1 to 30 carbon atoms,more preferably an acyl group having 1 to 20 carbon atoms, particularlypreferably an acyl group having 1 to 12 carbon atoms, and examplesthereof include acetyl, benzoyl, formyl, pivaloyl and the like), analkoxycarbonyl group (preferably an alkoxycarbonyl group having 2 to 30carbon atoms, more preferably an alkoxycarbonyl group having 2 to 20carbon atoms, particularly preferably an alkoxycarbonyl group having 2to 12 carbon atoms, and examples thereof include methoxycarbonyl,ethoxycarbonyl and the like), an aryloxycarbonyl group (preferably anaryloxycarbonyl group having 7 to 30 carbon atoms, more preferably anaryloxycarbonyl group having 7 to 20 carbon atoms, particularlypreferably an aryloxycarbonyl group having 7 to 12 carbon atoms, andexamples thereof include phenyloxycarbonyl and the like), an acyloxygroup (preferably an acyloxy group having 2 to 30 carbon atoms, morepreferably an acyloxy group having 2 to 20 carbon atoms, particularlypreferably an acyloxy group having 2 to 10 carbon atoms, and examplesthereof include acetoxy, benzoyloxy and the like), an acylamino group(preferably an acylamino group having 2 to 30 carbon atoms, morepreferably an acylamino group having 2 to 20 carbon atoms, particularlypreferably an acylamino group having 2 to 10 carbon atoms, and examplesthereof include acetylamino, benzoylamino and the like),an alkoxycarbonylamino group (preferably an alkoxycarbonylamino grouphaving 2 to 30 carbon atoms, more preferably an alkoxycarbonylaminogroup having 2 to 20 carbon atoms, particularly preferably analkoxycarbonylamino group having 2 to 12 carbon atoms, and examplesthereof include methoxycarbonylamino and the like), anaryloxycarbonylamino group (preferably an aryloxycarbonylamino grouphaving 7 to 30 carbon atoms, more preferably an aryloxycarbonylaminogroup having 7 to 20 carbon atoms, particularly preferably anaryloxycarbonylamino group having 7 to 12 carbon atoms, and examplesthereof include phenyloxycarbonylamino and the like), a sulfonylaminogroup (preferably a sulfonylamino group having 1 to 30 carbon atoms,more preferably a sulfonylamino group having 1 to 20 carbon atoms,particularly preferably a sulfonylamino group having 1 to 12 carbonatoms, and examples thereof include methanesulfonylamino,benzenesulfonylamino and the like), a sulfamoyl group (preferably asulfamoyl group having 0 to 30 carbon atoms, more preferably a sulfamoylgroup having 0 to 20 carbon atoms, particularly preferably a sulfamoylgroup having 0 to 12 carbon atoms, and examples thereof includesulfamoyl, methylsulfamoyl, dimethylsulfamoyl, phenylsulfamoyl and thelike),a carbamoyl group (preferably a carbamoyl group having 1 to 30 carbonatoms, more preferably a carbamoyl group having 1 to 20 carbon atoms,particularly preferably a carbamoyl group having 1 to 12 carbon atoms,and examples thereof include carbamoyl, methylcarbamoyl,diethylcarbamoyl, phenylcarbamoyl and the like), an alkylthio group(preferably an alkylthio group having 1 to 30 carbon atoms, morepreferably an alkylthio group having 1 to 20 carbon atoms, particularlypreferably an alkylthio group having 1 to 12 carbon atoms, and examplesthereof include methylthio, ethylthio and the like), an arylthio group(preferably an arylthio group having 6 to 30 carbon atoms, morepreferably an arylthio group having 6 to 20 carbon atoms, particularlypreferably an arylthio group having 6 to 12 carbon atoms, and examplesthereof include phenylthio and the like), a heterocyclic thio group(preferably a heterocyclic thio group having 1 to 30 carbon atoms, morepreferably a heterocyclic thio group having 1 to 20 carbon atoms,particularly preferably a heterocyclic thio group having 1 to 12 carbonatoms, and examples thereof include pyridylthio, 2-benzimizolylthio,2-benzoxazolylthio, 2-benzthiazolylthio and the like),a sulfonyl group (preferably a sulfonyl group having 1 to 30 carbonatoms, more preferably a sulfonyl group having 1 to 20 carbon atoms,particularly preferably a sulfonyl group having 1 to 12 carbon atoms,and examples thereof include mesyl, tosyl and the like), a sulfinylgroup (preferably a sulfinyl group having 1 to 30 carbon atoms, morepreferably a sulfinyl group having 1 to 20 carbon atoms, particularlypreferably a sulfinyl group having 1 to 12 carbon atoms, and examplesthereof include methanesulfinyl, benzenesulfinyl and the like), a ureidogroup (preferably a ureido group having 1 to 30 carbon atoms, morepreferably a ureido group having 1 to 20 carbon atoms, particularlypreferably a ureido group having 1 to 12 carbon atoms, and examplesthereof include ureido, methylureido, phenylureido and the like), aphosphoric acid amide group (preferably a phosphoric acid amide grouphaving 1 to 30 carbon atoms, more preferably a phosphoric acid amidegroup having 1 to 20 carbon atoms, particularly preferably a phosphoricacid amide group having 1 to 12 carbon atoms, and examples thereofinclude diethylphosphoric acid amide, phenylphosphoric acid amide andthe like), a hydroxyl group, a mercapto group, a halogen atom (forexample, a fluorine atom, a chlorine atom, a bromine atom and an iodineatom, more preferably a fluorine atom),a cyano group, a sulfo group, a carboxyl group, an oxo group, a nitrogroup, a hydroxamic acid group, a sulfino group, a hydrazino group, animino group, a heterocyclic group (preferably a 3- to 7-memberedheterocyclic group, which may be an aromatic or non-aromaticheterocyclic group, examples of a hetero atom constituting theheterocyclic group include a nitrogen atom, an oxygen atom and a sulfuratom, and preferably a heterocyclic group having 0 to 30 carbon atoms,more preferably a heterocyclic group having 1 to 12 carbon atoms, andspecifically examples of the heterocyclic group include imidazolyl,pyridyl, quinolyl, furyl, thienyl, piperidyl, morpholino, benzoxazolyl,benzimidazolyl, benzthiazolyl, carbazolyl, azepinyl and the like), asilyl group (preferably a silyl group having 3 to 40 carbon atoms, morepreferably a silyl group having 3 to 30 carbon atoms, particularlypreferably a silyl group having 3 to 24 carbon atoms, and examplesthereof include trimethylsilyl, triphenylsilyl and the like), a silyloxygroup (preferably a silyloxy group having 3 to 40 carbon atoms, morepreferably a silyloxy group having 3 to 30 carbon atoms, particularlypreferably a silyloxy group having 3 to 24 carbon atoms, and examplesthereof include trimethylsilyloxy, triphenylsilyloxy and the like) andthe like. These substituents may be further substituted by one or moresubstituents selected from the substituent group Z.

Herein, when one structural site has a plurality of substituents, thosesubstituents may be linked with each other to form a ring, or may besubjected to ring condensation partially or wholly with theabove-described structural site to form an aromatic ring or anunsaturated heterocycle.

Preferred specific examples of the polyimide compound are shown in thefollowings, but the present invention is not limited thereto.

TABLE 1 X Y Z P-1 60 32 8 P-2 60 32 8 P-3 50 42 8 P-4 60 35 5 P-5 83 107 P-6 30 62 8 P-7 70 25 5 P-8 60 35 5 P-9 50 10 40 P-10 50 47 3 P-11 4520 35 P-12 60 32 8 P-13 50 42 8 P-14 60 35 5 P-15 83 16 1 P-16 10 82 8P-17 90 7.5 2.5 P-18 60 32 8 P-19 60 32 8 P-20 40 52 8 P-21 45 50 5 P-2250 45 5 P-23 50 49 1 P-24 44 55.5 0.5 P-25 40 52 8 P-26 60 32 8 P-27 4025 35 P-28 35 20 45 P-29 60 32 8 P-30 60 32 8

Molar ratio in the above-described chemical formulas [ratio of X/Y/Zbased on 100 of a specific unit in the formula]

The polymer for use in the present invention may be a copolymer withother monomers. Examples of useful other monomers include known monomerssuch as acrylates, methacrylates, acrylamides, methacrylamides, vinylesters, styrenes, acrylic acid, methacrylic acid, acrylonitrile, maleicanhydride and maleic imide. By copolymerizing these monomers, variousphysical properties such as membrane-forming property, membranestrength, hydrophilicity, hydrophobicity, solubility, reactivity andstability can be improved. The synthesis of monomers is for examplecarried out with reference to ester synthesis of “5^(th) experimentscience lecture 16, organic synthesis (II-1)” or handling orpurification items of monomers of “5^(th) experiment science lecture 26,polymer chemistry” edited by the Japanese Chemical Society (issued byMaruzen Co. Ltd.).

The polyimide can be synthesized by condensation polymerization of anacid anhydride with a diamine As a synthetic method, a method describedin a general book (for example, Saishin Polyimide-Kiso to Oyo-, pp.3-49, edited by Yoshio Imai and Rikio Yokota, issued by NTS PublishingCo., Ltd.) can be appropriately selected. Specific examples of generalacid anhydride that can be used in the present invention are shownbelow. Herein, a commercial item may be used as P-19. Alternatively,P-19 can be synthesized with reference to JP-A-2006-219397.

Further, specific examples of general diamine are shown below.

The gas separation composite membrane according to the present inventioncan be formed by hardening due to a function of the radicallycrosslinkable functional group by providing the group with some sort ofenergy.

As a monomer corresponding to partial structure represented by Formula(I), (II-a), (II-b), (III-a) or (III-b), one processed into an oligomeror a prepolymer may be used. With regard to a polymer in obtaining apolymer compound, a copolymer having any form, such as a blockcopolymer, a random copolymer or a graft copolymer may be used. Inparticular, a case where a block copolymer or a graft copolymer is usedis preferred from viewpoints of viscosity and compatibility.

A ratio of partial structure represented by the above-described Formula(I), (II-a), (II-b), (III-a) or (III-b) is not particularly defined. Asa composition ratio of partial structure having a plurality ofcrosslinked structures increases, although an influence of molecularstructure is significant, strength of a membrane and separationselectivity are generally improved but gas permeability tends todecrease. Therefore, as the composition ratio, the range of from 1 to50% by mass, and preferably from 5 to 30% by mass is applied as acriterion, respectively. However, the composition ratio is not limitedto these ranges, and the composition ratio is changed according to thepurpose of gas separation (a recovery ratio, purity or the like), andthus gas permeability and separation selectivity are adjusted.

In the present invention, a ratio of copolymerization (R₁) of aconstitutional unit of Formula (I), a ratio of copolymerization (R_(II))of a constitutional unit of Formulas (II-a) and (II-b), and a ratio ofcopolymerization (R_(III)) of a constitutional unit of Formulas (III-a)and (III-b) are not particularly limited, but are preferably asdescribed below.

Particularly Preferred range More preferred range preferred range R_(II)from 0 to 90 mol % from 0 to 80 mol % from 0 to 60 mol % R_(III) from0.01 to 17 from 0.1 to 10 mol % from 1 to 10 mol % mol % R_(IV)* from0.01 to 90 from 0.1 to 90 mol % from 1 to 90 mol % mol % Note: R_(IV)with a symbol * is a ratio of copolymerization of any otherconstitutional unit, provided that an expression: R_(I) = R_(II) +R_(III) + R_(IV) should be satisfied in each preferred range of R_(I),R_(II), R_(III) and R_(IV).

The molecular weight of the above-described polyimide compound is notparticularly limited because of a crosslinked membrane. The molecularweight corresponding to each partial structure is preferably, as themass average molecular weight, from 1,000 to 1,000,000, more preferablyfrom 5,000 to 500,000, and further preferably from 5,000 to 100,000.

Unless it is explicitly stated otherwise, the molecular weight and thedegree of dispersion are defined as the values obtained by measurementin accordance with a GPC (Gel Permeation Chromatography). The molecularweight is defined as polystyrene-converted mass-average molecularweight. The gel charged into the column used in the GPC method ispreferably a gel having an aromatic compound as a repeating unit, andexamples thereof include a gel made of styrene-divinylbenzenecopolymers. The column is preferably used in the form where 2 to 6columns are connected. Examples of a solvent used include ether-basedsolvents such as tetrahydrofuran, and amide-based solvents such asN-methylpyrrolidinone. The measurement is preferably carried out at aflow rate of the solvent in the range of from 0.1 to 2 mL/min, and mostpreferably in the range of from 0.5 to 1.5 mL/min. By carrying out themeasurement within these ranges, there is no occurrence of loading in anapparatus, and thus, the measurement can be carried out furtherefficiently. The measurement temperature is preferably carried out atfrom 10° C. to 50° C., and most preferably from 20° C. to 40° C. Acolumn and a carrier to be used can be properly selected, according tothe property of a polymer compound to be measured.

[Crosslinked Polyimide Resin] (Crosslinked Site Ratio [η])

In the present invention, a ratio [η] of a crosslinked site to an imidegroup of the above-described polyimide compound (the number ofcrosslinked sites/the number of imide groups) in the above-describedcrosslinked polyimide resin is from 0.0001 to 0.45, preferably from 0.01to 0.3, more preferably from 0.01 to 0.2, and further preferably from0.01 to 0.1. Further, when the ratio is set to a low crosslinked siteratio, the ratio is preferably 0.05 or less, more preferably 0.04 orless, and particularly preferably 0.02 or less.

“Crosslinked site ratio [η]” herein is based on the number ofcrosslinked crosslinkable functional groups, and expressed in terms of acalculated value (ratio) from which the number of uncrosslinkedcrosslinkable functional groups is excluded, even when any crosslinkablefunctional group is introduced into the polyimide compound. Adjustmentof this value to the above-described lower limit or more allowsminimization of a decrease in separation selectivity under high CO₂concentration conditions or in association with plasticizing of themembrane under the influence of an aromatic compound such as benzene,toluene and xylene contained in a natural gas, or hydrocarbon impuritiessuch as hexane and heptane contained therein. Adjustment of this valueto the above-described upper limit or less allows minimization of adecrease in gas permeability in association with an improvement ofcrosslinked density, and also an improvement of a crack or mechanicalstrength such as brittleness during bending.

Adjustment of this crosslinked site ratio to a desired range can beperformed by appropriately adjusting, during a synthesis of thepolyimide compound, an existence ratio of a crosslinkable functionalgroup (for example, later-mentioned crosslinkable functional groupdensity [γ]) or a crosslinking conversion ratio (for example, a ratio ofthe number of crosslinked functional groups based on the gross number ofcrosslinkable functional groups (crosslinking conversion ratio) [α]) bychanging crosslinking reaction conditions, and according to acalculation, an expression: [α]=[γ]×[α]/200 is satisfied. Specifically,the crosslinked site ratio [η] can be improved by increasing acomposition ratio of a monomer having a crosslinkable site in apredetermined range, enhancing reactivity, achieving polyfunctionality,or using a raw material having another crosslinkable substituent incombination.

(Crosslinked Structure)

In the present invention, with regard to the crosslinked polyimideresin, the crosslinked structural site (a structural site in which theabove-described radically crosslinkable functional group is crosslinked)preferably includes a linking group represented by —C(R^(A1))₂CH₂—[wherein R^(A1) represents a hydrogen atom, an alkyl group having 1 to10 carbon atoms, —R^(A2)—C(═O)O— or —R^(A2)—OC(═O)—; and R^(A2)represents an alkylene group having 1 to 10 carbon atoms].

Above all, R^(A1) is more preferably a hydrogen atom, —R^(A2)—C(═O)O— or—R^(A2)—OC(═O)— (wherein R^(A2) represents an alkylene group having 1 to5 carbon atoms).

Moreover, the crosslinked structural site is preferably crosslinked asdescribed below.

Herein, R^(B1) to R^(B4) each independently represent a hydrogen atom oran alkyl group having 1 to 10 carbon atoms.

The above-described crosslinked structural site is preferably (CL-1) or(CL-3), and more preferably (CL-1).

Specific examples of the structure of the above-described crosslinkedsite in relation with the crosslinkable functional group are asdescribed below. However, the present invention is in no way construedby being limited to these examples.

(Crosslinkable Functional Group Density [γ])

A ratio of the number of functional groups L² of Formulas (III-a) and(III-b) to the repeating unit represented by Formula (I) is referred toas crosslinkable functional group density [γ]. A preferred range of thisγ (the number of functional groups L²'s/the number of repeating unitsrepresented by Formula (I)) is from 0.003 to 0.68, and a furtherpreferred range is from 0.003 to 0.56.

This crosslinkable functional group density can be adjusted by an amountof charging a substrate (monomer) on synthesizing the polyimidecompound.

(Crosslinking Conversion Ratio [α])

The crosslinking conversion ratio [α] in the present invention can becalculated by a decrease of peaks of double bond sites (1640, 810 cm⁻¹)before and after crosslinking in reflective infrared spectroscopymeasurement of the membrane and a decrease of peaks of double bondsbefore and after crosslinking in ¹H-NMR. The crosslinking conversionratio is preferably 20% or more and 100% or less, more preferably 50% ormore and 94% or less, and further preferably 30% or more and 89% orless.

This crosslinking conversion ratio can be adjusted by conditions ofcrosslinking the polyimide compound, for example, by adjusting a kind ofa radical polymerization initiator, temperature in the crosslinkingreaction, a substrate concentration, an amount of heat, and an amount oflight and irradiation time of active radiation. Specific examplesinclude, in order to enhance a rate of reaction in the crosslinkingreaction in radical polymerization, increasing gross energy of heat orlight energy, and for a material, improving activity of a photoinitiator(e.g., a ketone-based compound) or a thermal initiator (e.g., a compoundhaving a low decomposition temperature for an azo compound), each beinga polymerization initiator.

[Method of Producing Gas Separation Composite Membrane]

The method of producing a gas separation composite membrane according tothe present invention preferably includes a production method by which amembrane is formed by coating a coating liquid containing theabove-described polyimide compound onto a support, and irradiating theresultant coated membrane with active radiation. The componentcomposition of the coating liquid (dope) for constituting the coatedmembrane is not particularly limited, but preferably contains theabove-described polyimide compound and a polymerization initiator in anorganic solvent. The content of the polyimide compound is notparticularly limited, but the compound is contained in the coatingliquid in an amount of preferably from 0.1 to 30% by mass, and furtherpreferably from 1 to 10% by mass. Adjustment of the content to theabove-described lower limit or more causes, when the concentration isweak, an increase in possibility of producing a defect on a surfacelayer contributing to separation due to easy permeation into a lowerlayer upon forming the membrane on the porous support. Adjustment of thecontent to the above-described upper limit or lower allows minimizationof a phenomenon of thin layer formation or a decrease in permeability ascaused by being packed in pores with high concentration upon forming themembrane on the porous support in the case of a high concentration. Thegas separation composite membrane according to the present invention canbe suitably produced by adjusting the molecular weight, structure andthe composition of the polymer in the separating layer, and alsosolution viscosity of the polymer.

[Organic Solvent]

The organic solvent is not particularly limited, and specific examplesinclude hydrocarbon-based organic solvents such as n-hexane andn-heptane; ester-based organic solvents such as methyl acetate, ethylacetate, and butyl acetate; lower alcohols such as methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol;aliphatic ketones such as acetone, methyl ethyl ketone, methyl isobutylketone, diacetone alcohol, cyclopentanone, and cyclohexanone;ether-based organic solvents such as ethylene glycol, diethylene glycol,triethylene glycol, glycerin, propylene glycol, ethylene glycolmonomethyl or monoethyl ether, propylene glycol methyl ether,dipropylene glycol methyl ether, tripropylene glycol methyl ether,ethylene glycol phenyl ether, propylene glycol phenyl ether, diethyleneglycol monomethyl or monoethyl ether, diethylene glycol monobutyl ether,triethylene glycol monomethyl or monoethyl ether, dibutyl butyl ether,tetrahydrofuran, methyl cyclopentyl ether, and dioxane;N-methylpyrrolidone, 2-pyrrolidone, dimethylformamide, dimethylimidazolidinone, dimethyl sulfoxide, dimethyl acetamide and the like.These organic solvents are suitably selected within the range in whichthe solvents do not exert a harmful influence, such as corrosion of thesupport, and preferably an ester-based solvent (preferably butylacetate), an alcohol-based solvent (preferably methanol, ethanol,isopropanol, and isobutanol), aliphatic ketones (preferably methyl ethylketone, methyl isobutyl ketone, diacetone alcohol, cyclopentanone, andcyclohexanone) or an ether type solvent (e.g., ethylene glycol,diethylene glycol monomethyl ether, and methyl cyclopentylether); andfurther preferably an aliphatic ketone-based solvent, an alcohol-basedsolvent or an ether-based solvent. These compounds may be used alone orin combination of two or more types.

The gas separation composite membrane preferably contains thelater-mentioned polymerization initiator and is formed by hardening byirradiation with active radiation. Here, the active radiation is notparticularly limited so long as it produces energy capable of generatinginitiation species in the membrane composition when irradiated andbroadly includes α-ray, γ-ray, X-rays, ultraviolet rays, visible rays,electric beams and the like. Of these, ultraviolet rays and electricbeams are preferred and ultraviolet rays are particularly preferred, interms of curing sensitivity and easy availability of apparatuses.

When ultraviolet rays are used in the present invention, addition of thefollowing photopolymerization initiator is necessary. Electric beamcuring is preferred since a polymerization initiator is unnecessary anda permeation depth is large. An electric beam accelerator may utilize ascanning manner, a double scanning manner or a curtain beam manner andis preferably a curtain beam manner capable of obtaining high power at arelatively low cost. Regarding properties of electric beam, anacceleration voltage is from 30 to 1000 kV, preferably from 50 to 300kV. An absorbed dose is preferably from 5 to 200 kGy (from 0.5 to 20Mrad), more preferably from 20 to 100 kGy (from 2 to 10 Mrad). When theacceleration voltage and absorbed dose are within these ranges, asufficient amount of energy is permeated and energy efficiency is thusgood. Regarding the atmosphere, at which an electric beam is irradiated,an oxygen concentration is preferably 200 ppm or less under a nitrogenatmosphere. Within this range, cross-linkage and curing are wellperformed around the surface.

A mercury lamp is used as a light source of ultraviolet rays. Themercury lamp utilizes a lamp of from 20 to 240 W/cm² and is used at aspeed of from 0.3 to 20 m/min The distance between the membrane and themercury lamp is preferably generally from 1 to 30 cm. When adesktop-type ultraviolet ray curing apparatus is used, curing ispreferably performed after suitably controlling light amount andposition of light source according to the material and environments forfrom about 1 second to about 10 minutes.

Known radiation curing apparatuses, conditions and the like described in“UV-EB curing techniques” (issued by Technical Integration Center,Corp.) or “Application techniques of low-energy electric beamirradiation” (2000, issued by CMC Co., Ltd.) and the like may be used.Curing may be carried out in conjunction with heating.

[Polymerization Initiator]

In the process of forming the gas separation composite membrane of thepresent invention, a radical polymerization initiator is preferablyadded and a photopolymerization initiator is particularly preferablyadded.

The photopolymerization initiator is a compound that causes chemicalreaction via action of light or interaction with a sensitizing dye in anelectron-excited state and thus produces at least one kind of radicals,acid and base.

The photopolymerization initiator may be appropriately selected fromthose having a sensitivity with respect to irradiated active radiationsuch as ultraviolet rays of from 400 to 200 nm, far ultraviolet rays,g-rays, h-rays, i-rays, KrF excimer laser beam, ArF excimer laser beam,electron beam, X-rays, molecular beam or ion beam.

Specifically, the photopolymerization initiator may be selected fromthose known to those skilled in the art without limitation and specificexamples thereof include the compounds described in Bruce M. Monroe etal., Chemical Review, 93, 435 (1993), R. S, Davidson, Journal ofPhotochemistry and biology A: Chemistry, 73, 81 (1993), J. P. Faussier,“Photonitiated Polymerization—Theory and Applications”: Rapra ReviewVol. 9, Report, Rapra Technology (1998), and M. Tsunooka et al., Prog.Polym. Sci., 21, 1 (1996). It is also possible to use the compounds forchemically amplified photoresists or photocation polymerizationdescribed in “Organic Materials for Imaging”, edited by the JapaneseResearch Association for Organic Electronics Materials, published byBunshin Design Printing Publishing and Digital Communications (1993),pp. 187-192. Further, compounds that cause bond cleavage in oxidative orreductive manner via interaction with a sensitizing dye in anelectron-excited state are also known, such as those described in F. D.Saeva, Topics in Current Chemistry, 156, 59 (1990), G. G. Maslak, Topicsin Current Chemistry, 168, 1 (1993), H. B. Shuster et al., J. Am. Chem.Soc., 112, 6329 (1990), and I. D. F. Eaton et al., J. Am. Chem. Soc.,102, 3298 (1980).

Preferred examples of the photopolymerization initiator include (a)aromatic ketones, (b) aromatic onium salt compounds, (c) organicperoxides, (d) hexaaryl biimidazole compounds, (e) ketoxime estercompounds, (f) borate compounds, (g) azinium compounds, (h) metallocenecompounds, (i) active ester compounds, and (j) compounds having acarbon-halogen bond.

Preferred examples of the (a) aromatic ketones include the compoundshaving a benzophenone skeleton or a thioxanthone skeleton described inJ. P. Fouassier and J. F. Rabek, “Radiation Curing in Polymer Scienceand Technology” (1993), pp. 77-117. More preferred examples of the (a)aromatic ketones include α-thiobenzophenone compounds described inJP-B-47-6416 (“JP-B” means examined Japanese patent publication),benzoin ether compounds described in JP-B-47-3981, α-substituted benzoincompounds described in JP-B-47-22326, benzoin derivatives described inJP-B-47-23664, aroyl phosphonates described in JP-A-57-30704,dialkoxybenzophenones described in JP-B-60-26483, benzoin ethersdescribed in JP-B-60-26403 and JP-A-62-81345, α-aminobenzophenonesdescribed in JP-B-1-34242, U.S. Pat. No. 4,318,791 and EP 0284561 A1,p-di(dimethylaminobenzoyl)benzenes described in JP-A-2-211452,thio-substituted aromatic ketones described in JP-A-61-194062,acylphosphinesulfide described in JP-B-2-9597, acylphosphine describedin JP-B-2-9596, thioxanthones described in JP-B-63-61950, and coumarinsdescribed in JP-B-59-42864.

The (b) aromatic omium salts include aromatic omium salts of elements ofGroups V, VI and VII of the periodic table, and more specifically, N, P,As, Sb, Bi, O, S, Se, Te or I. Preferred examples of the (b) aromaticomium salts include: iodonium salts described in European Patent No.104143, U.S. Pat. No. 4,837,124, JP-A-2-150848 and JP-A-2-96514;sulfonium salts described in European Patent No. 370693, European PatentNo. 233567, European Patent No. 297443, European Patent No. 297442,European Patent No. 279210, European Patent No. 422570, U.S. Pat. No.3,902,144, U.S. Pat. No. 4,933,377, U.S. Pat. No. 4,760,013, U.S. Pat.No. 4,734,444 and U.S. Pat. No. 2,833,827; diazonium salts (such asbenzene diazonium which may contain a substituent); resins of diazoniumsalts (such as formaldehyde resins of diazo diphenylamine); N-alkoxypyrridium salts (such as those described in U.S. Pat. No. 4,743,528,JP-A-63-138345, JP-A-63-142345, JP-A-63-142346 and JP-B-46-42363, andmore specifically 1-methoxy-4-phenyl pyrridium tetrafluoroborate); andcompounds described in JP-B-52-147277, JP-B-52-14278 and JP-B-52-14279.These salts produce radicals or acids as the active species.

The (c) “organic peroxides” described above include almost all organiccompounds having one or more oxygen-oxygen bonds in the molecule, andpreferred examples thereof include peroxide esters such as3,3′,4,4′-tetra-(t-butylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra-(t-amylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra-(t-hexylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra-(t-octylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra-(cumylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra-(p-iso-propylcumylperoxycarbonyl)benzophenone, anddi-t-butyl di-peroxy isophthalate.

Examples of the (d) hexaaryl biimidazoles mentioned above includelophine dimers described in JP-B-45-37377 and JP-B-44-86516, such as2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-bromophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o,p-dichloro-phenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetra-(m-methoxyphenyl)biimidazole,2,2′-bis(o,o′-dichloro-phenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-nitrophenyl)-4,4′,5,5′-tetraphenyl biimidazole,2,2′-bis(o-methyl-phenyl)-4,4′,5,5′-tetraphenyl biimidazole, and2,2′-bis(o-trifluoro-phenyl)-4,4′,5,5′-tetraphenyl biimidazole.

Examples of the (e) ketoxium esters include3-benzoyloxy-iminobutan-2-one, 3-acetoxy-iminobutan-2-one,3-propionyloxy-iminobutan-2-one, 2-acetoxy-iminopentan-3-one,2-acetoxyimino-1-phenylpropan-1-one,2-benzoyloxyimino-1-phenylpropan-1-one, 3-p-toluene sulfonyloxyiminobutan-2-one, and 2-ethoxycarbonyl oxyimino-1-phenylpropan-1-one.

Examples of the (f) borate salts include the compounds described in U.S.Pat. No. 3,567,453, U.S. Pat. No. 4,343,891, European Patent No. 109772and European Patent No. 109773.

Examples of the (g) azinium salt compounds include compounds having N-0bond described in JP-A-63-138345, JP-A-63-142345, JP-A-63-142346,JP-A-63-143537 and JP-B-46-42363.

Examples of the (h) metallocene compounds include titanocene compoundsas described in JP-A-59-152396, JP-A-61-151197, JP-A-63-41484,JP-A-2-249, and JP-A-2-4705, and iron-arene complexes described inJP-A-1-304453 and JP-A-1-152109.

Specific examples of the aforementioned titanocene compound includedi-cyclopentadienyl-Ti-di-chloride, di-cyclopentadienyl-Ti-bis-phenyl,di-cyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,6-di-fluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,4-di-fluorophen-1-yl,di-methyl-cyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,di-methyl-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,di-methyl-cyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,bis(cyclopentadienyl)-bis(2,6-difluoro-3-(pyr-1-yl)phenyl)titanium,bis(cyclopentadienyl)bis[2,6-difluoro-3-(methyl-sulfonamide)phenyl]titanium,and bis(cyclopentadienyl)bis[2,6-difluoro-3-(N-butylbiaroyl-amino)phenyl]titanium.

Examples of the (i) active ester compounds include nitrobenzyl estercompounds described in European Patent No. 0290750, European Patent No.046083, European Patent No. 156153, European Patent No. 271851, EuropeanPatent No. 0388343, U.S. Pat. No. 3,901,710, U.S. Pat. No. 4,181,531,JP-A-60-198538, and JP-A-53-133022; iminosulfonate compounds describedin European Patent No. 0199672, European Patent No. 84515, EuropeanPatent No. 199672, European Patent No. 044115, European Patent No.0101122, U.S. Pat. No. 4,618,564, U.S. Pat. No. 4,371,605, U.S. Pat. No.4,431,774, JP-A-64-18143, JP-A-2-245756, and JP-A-4-365048; andcompounds described in JP-B-62-6223, JP-B-63-14340 and JP-A-59-174831.

Examples of the (j) compounds containing a carbon-halogen bond include acompound as described by Wakabayashi, et al., in Bull. Chem. Soc. Japan,42, 2924 (1969), a compound described in GB Patent No. 1388492, acompound described in JP-A-53-133428, and a compound as described inGerman Patent No. 3337024.

Other examples include a compound described by F. C. Schaefer, et. al.,in J. Org. Chem., 29, 1527 (1964), a compound described inJP-A-62-58241, and a compound described in JP-A-5-281728. Other examplesinclude a compound described in German Patent No. 2641100, a compounddescribed in German Patent No. 3333450, a group of compounds describedin German Patent No. 3021590, and a group of compounds described inGerman Patent 3021599.

The amount of used polymerization initiator is preferably from 0.01 masspart to 10 mass parts, more preferably from 0.1 mass part to 5 massparts, based on 1 mass part of the polymerizable compound.

[Cosensitizer]

A known compound having a function of further improving sensitivity orsuppressing polymerization inhibition due to oxygen may be added as acosensitizer in the process of producing the gas separation compositemembrane of the present invention.

Examples of such a cosensitizer include amines such as the compoundsdescribed in M. R. Sander et al., “Journal of Polymer Society”, Vol. 10,p. 3173 (1972), JP-B-44-20189, JP-A-51-82102, JP-A-52-134692,JP-A-59-138205, JP-A-60-84305, JP-A-62-18537, JP-A-64-33104 and ResearchDisclosure Vol. 33825. Specific examples include triethanolamine, ethylp-dimethylaminobenzoate, p-formyldimethylaniline andp-methylthiodimethylaniline.

Examples of other cosensitizers include thiols and sulfides, such asthiol compounds described in JP-A-53-702, JP-B-55-500806 andJP-A-5-142772 and disulfide compounds described in JP-A-56-75643.Specific examples include 2-mercaptobenzothiazole,2-mercaptobenzoxazole, 2-mercaptobenzimidazole,2-mercapto-4(3H)-quinazoline, and β-mercaptonaphthalene.

Other examples of the cosensitizer include amino acid compounds (such asN-phenylglycine), organic metal compounds (such as tributyltin acetate)described in JP-B-48-42965, hydrogen donors described in JP-B-55-34414,sulfur compounds (such as trithian) described in JP-A-6-308727,phosphorous compounds (such as diethyl phosphite) described inJP-A-6-250387, and Si—H and Ge—H compounds described in JP-A-8-65779.

[Other Components and the Like]

The gas separation composite membrane of the present invention maycontain a variety of polymer compounds in order to adjust membranephysical properties. Examples of the polymer compounds includeacryl-based polymers, polyurethane resins, polyamide resins, polyesterresins, epoxy resins, phenol resins, polycarbonate resins, polyvinylbutyral resins, polyvinyl formal resins, shelac, vinyl-based resins,acryl-based resins, rubber-based resins, waxes, and other naturalresins. These resins may be used alone or in combination of two or morekinds thereof.

Moreover, a nonionic surfactant, a cationic surfactant, an organicfluoro surfactant or the like may be added in order to adjust liquidphysical properties.

Specific examples of the surfactant include anionic surfactants such asalkylbenzene sulfonates, alkyl naphthalene sulfonates, higher fatty acidsalts, sulfonates of a higher fatty acid ester, ester sulfates of ahigher alcohol ether, sulfonates of a higher alcohol ether,alkylcarboxylates of a higher alkylsulfone amide, and alkylphosphates;and nonionic surfactants such as polyoxyethylene alkyl ethers,polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters,sorbitan fatty acid esters, ethylene oxide adducts of acetylene glycol,ethylene oxide adducts of glycerin, and polyoxyethylene sorbitan fattyacid esters. Other examples include amphoteric surfactants such as alkylbetaine or amide betaine, silicone-based surfactants, fluorine-basedsurfactants and the like. The surfactant may be suitably selected fromconventionally known surfactants and derivatives thereof.

Specific examples of polymer dispersants include polyvinyl pyrrolidone,polyvinyl alcohol, polyvinyl methylether, polyethylene oxide,polyethylene glycol, polypropylene glycol, and polyacryl amide. Amongthem, polyvinyl pyrrolidone is preferably used.

The conditions to form the gas separation composite membrane of thepresent invention are not particularly limited, but the temperature ispreferably from −30° C. to 100° C., more preferably from −10° C. to 80°C., and particularly preferably from 5° C. to 50° C.

In the present invention, gas such as air or oxygen may coexist duringformation of membrane, but the formation is preferably performed underan inert gas atmosphere.

Moreover, an organic solvent may be added as a medium used for formingthe gas separation composite membrane of the present invention.Specifically, organic solvents to be used are not particularly limited,but examples include hydrocarbon-based organic solvents such as n-hexaneand n-heptane; ester-based organic solvents such as methyl acetate,ethyl acetate, and butyl acetate; lower alcohols such as methanol,ethanol, n-propanol, isopropanol, n-butanol, isobutanol andtert-butanol; aliphatic ketones such as acetone, methyl ethyl ketone,methyl isobutyl ketone and diacetone alcohol; ether-based organicsolvents such as ethylene glycol, diethylene glycol, triethylene glycol,glycerin, propylene glycol, ethylene glycol monomethyl or monoethylether, propylene glycol methyl ether, dipropylene glycol methyl ether,tripropylene glycol methyl ether, ethylene glycol phenyl ether,propylene glycol phenyl ether, diethylene glycol monomethyl or monoethylether, diethylene glycol monobutyl ether, triethylene glycol monomethylor monoethyl ether, dibutyl ether and tetrahydrofuran;N-methylpyrrolidone, 2-pyrrolidone, dimethylformamide, dimethylimidazolidinone, dimethyl sulfoxide, dimethyl acetamide and the like.These compounds may be used alone or in combination of two or moretypes.

The membrane thickness of the gas separation composite membrane of thepresent invention is preferably from 0.01 to 100 μm, more preferablyfrom 0.1 to 10 μm.

[Method of Separating Gas Mixture]

The method of separating a gas mixture according to the presentinvention is a method of separating at least one acid gas from a mixedgas containing the at least one acid gas. The acid gas that can beseparated by using the gas separation composite membrane of the presentinvention is preferably carbon dioxide or hydrogen sulfide.

In the method of separating gas using the gas separation compositemembrane of the present invention, the components of gas mixture of rawmaterials are not particularly restricted, but main components of thegas mixture are preferably carbon dioxide and methane or carbon dioxideand hydrogen. When the gas mixture is present together with an acid gassuch as carbon dioxide or hydrogen sulfide, a method of separating gasusing the gas separation membrane of the present invention exertsconsiderably superior performance, preferably exerts superiorperformance for separation of carbon dioxide and hydrocarbon such asmethane, carbon dioxide and nitrogen, or carbon dioxide and hydrogen.

[Gas Separation Membrane Module and Gas Separation Apparatus]

The gas separation membrane of the present invention is a compositemembrane using a porous support in combination, and a gas separationmembrane module using the same is preferred. Moreover, an apparatus forgas separation having means for separating and recovering or separatingand purifying gas can be obtained by using the gas separation compositemembrane or gas separation membrane module of the present invention.

The gas separation composite membrane of the present invention ispreferably used in the form of a module. Examples of the module includespiral, hollow, pleat, tubular, and plate and frame type. Moreover, thegas separation composite membrane of the present invention may beapplied to an apparatus for separating and recovering gas using amembrane/absorption hybrid method in conjunction with an absorptionsolution, for example, as described in JP-A-2007-297605.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to examples, but the present invention is not limited to theseexamples. In addition, “part” and “%” is based on mass, unless otherwiseparticularly described.

Synthesis Examples Synthesis of Monomers (M-2) and (M-5)

The monomers (M-2) and (M-5) were synthesized, in accordance with thefollowing reaction scheme.

Herein, “Me” represents a methyl group, “Et” represents an ethyl group,“IPA” represents isopropyl alcohol, and “NMP” representsN-methylpyrrolidone.

Synthesis of Compound (M-1)

Into a 3 L three-necked flask, 130.14 g (1.0 mol) of 2-hydroxyethylmethacrylate (product number: 086-04385, manufactured by Wako PureChemical Industries, Ltd.) and 260 mL of acetonitrile were put, theresultant mixture was stirred under a nitrogen flow and underice-cooling, and thereto, an acetonitrile solution (460 mL) of 230.56 g(1.0 mol) of 3,5-dinitrobenzoyl chloride (product number: D0825,manufactured by Tokyo Chemical Industry Co., Ltd.) was added. Further,146.5 mL (1.05 mmol) of triethylamine (product number: 292-02656,manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwisethereto over 30 minutes or more. After completion of the dropwiseaddition, the resultant mixture was stifled for 1 hour underice-cooling, and then gradually heated to room temperature. Water wasadded to the resultant reaction mixture, produced crystals werefiltered, and then collected crude crystals were washed with ionexchange water and methanol, and thus 297.5 g of compound (M-1) wasobtained. (Yield: 92%.) The compound (M-1) was used for the nextreaction without further purification.

¹H-NMR (300 MHz) δ=9.25 (br.t, J=2.1 Hz, 1H), 9.17 (br.d, J=2.1 Hz, 2H),6.15-6.17 (m, 1H), 5.65-5.62 (m, 1H), 4.50-4.62 (m, 2H), 4.70-4.80 (m,2H), 1.96 (s, 3H)

Synthesis of Compound (M-2)

Into a 3 L three-necked flask, 307.5 g (5.51 mol) of reduced iron(product number: 096-00785, manufactured by Wako Pure ChemicalIndustries, Ltd.), 49.1 g (0.92 mol) of ammonium chloride (productnumber: 018-20985, manufactured by Wako Pure Chemical Industries, Ltd.),1,230 mL of 2-propanol, and 250 mL of water were put, and the resultantmixture was stirred under heating reflux. When heating reflux wasconfirmed, 49 mL of glacial acetic acid was added thereto, and theresultant mixture was stirred for 5 minutes under heating reflux, andthen 297.53 g (0.918 mol) of the compound (M-1) was carefully addedthereto, and the resultant mixture was further stirred for 2 hours underheating reflux. The resultant reaction mixture was cooled to vicinity ofroom temperature, and then 2 L of methanol was added thereto, an ironresidue was removed by performing Celite filtration, and a filtrate wasconcentrated by a rotary evaporator. Ethyl acetate was added to theconcentrate, and the resultant mixture was purified by silica gel columnchromatography, and subjected to recrystallization from a hexane-ethylacetate mixed solution, and thus 134.6 g of compounds (M-2) wasobtained. (Yield: 56%)

¹H-NMR (300 MHz) δ=6.78 (br.d, J=2.1 Hz, 2H), 6.19 (br.t, J=2.1 Hz, 1H),6.12-6.16 (m, 1H), 4.48-4.54 (m, 2H), 4.43-4.48 (m, 2H), 1.95 (s, 3H)

Synthesis of Compound (M-3)

Into a 500 mL three-necked flask, 13.72 g (0.10 mol) of4-amino-3,5-xylenol (product number: A 1860, manufactured by TokyoChemical Industry Co., Ltd.), 41 mL of N-methylpyrrolidone, and 41 mL ofacetonitrile were put, the resultant mixture was stirred under anitrogen flow and under ice-cooling, and thereto, 14.7 mL (1.0 mol) oftriethylamine (product number: 292-02656, manufactured by Wako PureChemical Industries, Ltd.) was added. Further, 30 mL of an acetonitrilesolution of 23.06 g (0.10 mol) of 3,5-dinitrobenzoyl chloride (productnumber: D0825, manufactured by Tokyo Chemical Industry Co., Ltd.) wasadded dropwise thereto over 30 minutes or more. After completion of thedropwise addition, the resultant mixture was stirred for 1 hour underice-cooling, and then gradually heated to room temperature. Water wasadded to the resultant reaction mixture, produced crystals werefiltered, and then collected crude crystals were washed with ionexchange water and acetonitrile-H₂O (1:1), and thus 14.6 g of compound(M-3) was obtained. (Yield: 44%). The compound (M-3) was used for thenext reaction without further purification.

Synthesis of Compound (M-4)

Into a 500 mL three-necked flask, 9.5 g (0.029 mol) of compound (M-3)and 180 mL of acetonitrile were put, the resultant mixture was stirredunder a nitrogen flow and under ice-cooling, and thereto, 4.4 mL (0.032mol) of triethylamine (product number: 292-02656, manufactured by WakoPure Chemical Industries, Ltd.) was added. Further, an acetonitrilesolution (30 mL) of 3.0 g (0.029 mol) of methacryloyl chloride (productnumber: 130-11742, manufactured by Tokyo Chemical Industry Co., Ltd.)was added dropwise thereto over 30 minutes or more. After completion ofthe dropwise addition, the resultant mixture was stirred for 1 hourunder ice-cooling, and then gradually heated to room temperature. Waterwas added to the resultant reaction mixture, produced crystals werefiltered, and then collected crude crystals were washed with ionexchange water and acetonitrile-H₂O (1:1), and thus 7.2 g of compound(M-4) was obtained. (Yield: 52%). The compound (M-4) was used for thenext reaction without further purification.

Synthesis of Monomer (M-5)

Into a 500 mL three-necked flask, 13.0 g (mol) of reduced iron (productnumber: 096-00785, manufactured by Wako Pure Chemical Industries, Ltd.),1.3 g (mol) of ammonium chloride (product number: 018-20985,manufactured by Wako Pure Chemical Industries, Ltd.), 130 mL of2-propanol, and 250 mL of water were put, and the resultant mixture wasstirred under heating reflux. When heating reflux was confirmed, 1.3 mLof glacial acetic acid was added thereto, and the resultant mixture wasstirred for 5 minutes under heating reflux, and then 13.0 g (mol) of thecompound (M-4) was carefully added thereto, and the resultant mixturewas further stirred for 2 hours under heating reflux. The resultantreaction mixture was cooled to vicinity of room temperature, and then0.5 L of ethyl acetate was added thereto, an iron residue was removed byperforming Celite filtration, and a filtrate was concentrated by arotary evaporator. Ethyl acetate was added to the concentrate, and theresultant mixture was purified by silica gel column chromatography, andsubjected to recrystallization from a hexane-ethyl acetate mixedsolution, and thus 7.01 g of compounds (M-5) was obtained. (Yield: 63%)

¹H-NMR (300 MHz) δ=9.35 (br.s, 1H), 6.91 (br. 2H), 6.35 (br.d, J=2.1 Hz,2H), 6.26 (br.s, 1H), 5.99 (br, 1H), 5.89 (br, 1H), 4.92 (br.s, 4H),2.16 (s, 6H), 2.00 (s, 3H)

Synthesis Example Synthesis of Polymer (P-1)

The polymer (P-1) was synthesized, in accordance with the followingreaction scheme.

Synthesis of Polymer (P-1)

Into a 1 L three-necked flask, 123 mL of N-methylpyrrolidone and 54.97 g(0.124 mol) of 6FDA (product number: H0771, manufactured by TokyoChemical Industry Co., Ltd.) were put to allow dissolution at 40° C.,the resultant mixture was stirred under a nitrogen flow, and thereto,87.2 mL of N-methylpyrrolidone solution containing 12.19 g (0.074 mol)of 2,3,5,6-tetramethylphenylenediamine (product number: T1457,manufactured by Tokyo Chemical Industry Co., Ltd.), 4.28 g (0.040 mol)of m-phenylenediamine (product number: P0169, manufactured by TokyoChemical Industry Co., Ltd.), 2.64 g (0.01 mol) of the monomer (M-2) andIrganox 1010 (0.132 g) was added dropwise thereto over 30 minutes whilekeeping an inside of a system at 40° C. The resultant reaction mixturewas stirred at 40° C. for 2.5 hours, and then 2.94 g (0.037 mol) ofpyridine (product number: 166-22575, manufactured by Wako Pure ChemicalIndustries, Ltd.) and 31.58 g (0.31 mol) of acetic anhydride (productnumber: 018-00286, manufactured by Wako Pure Chemical Industries, Ltd.)were added thereto, respectively, and the resultant mixture was stirredat 80° C. for 3 hours. Then, 676.6 mL of acetone was added to thereaction mixture, and the reaction mixture was diluted. Into a 5 Lstainless steel container, 1.15 L of methanol and 230 mL of acetone wereput, the resultant mixture was stirred, and thereto, the acetone dilutedsolution of the reaction mixture was added dropwise. A precipitatedpolymer was subjected to suction filtration, and air blow drying at 60°C., and thus 62.3 g of polymer (P-1) was obtained.

Example 1

In a 30 mL brown vial, 1.4 g of polymer (P-1) and 8.6 g of methyl ethylketone were mixed, the resultant mixture was stirred for 30 minutes, 28mg of 1-hydroxycyclohexyl phenyl ketone (product number: 40, 561-2,manufactured by Sigma-Aldrich Corporation) was further added thereto,and the resultant mixture was stirred for 30 minutes. On a 10 cm squareclean glass plate, a polyacrylonitrile porous membrane (manufactured byGMT Membrantechnik GmbH) was left to stand, the polymer liquid was caston a surface of the porous support membrane using an applicator, and theresultant material was immediately exposed at 10 mW for 60 seconds usinglight curing apparatus (TCT1000B-28HE) manufactured by Sen LightsCorporation, and thus a composite membrane sample No. 101 was obtained.The thickness of polymer (P-1) layer was about 1 μm, and the thicknessof the polyacrylonitrile porous membrane, including a nonwoven fabric,was about 180 μm.

Synthesis of Polymers (P-1A) and (P-1B), and Production of Sample Nos.102 and 103

Composite membranes were produced in a manner similar to the productionof the composite membrane sample No. 101 except that, in a synthesis ofthe above-described polymer P-1, the amount of 4.28 g (0.040 mol) ofm-phenylenediamine was changed to 5.03 g (0.0465 mol) or 5.33 g (0.0493mol), and the amount of 2.64 g (0.01 mol) of the monomer (M-2) waschanged to 0.925 g (0.0035 mol) or 0.183 g (0.00074 mol) [sample Nos.102(P-1A) and 103(P-1B)].

Synthesis of Polymer (P-1C), and Production of Sample No. 104

A composite membrane was produced in a manner similar to the productionof the composite membrane sample No. 101 except that, in a synthesis ofthe above-described polymer P-1, the amount of 12.19 g (0.074 mol) of2,3,5,6-tetramethylphenylenediamine was changed to 6.57 g (0.040 mol),the amount of 4.28 g (0.040 mol) of m-phenylenediamine was changed to 0g, and the amount of 2.64 g (0.01 mol) of the monomer (M-2) was changedto 22.20 g (0.084 mol) [sample No. 104(P-1C)].

A composite membrane No. sample 105 was produced in a manner similar tothe production of the composite membrane sample No. 101 except thatexposure time was changed from 60 seconds to 5 seconds.

Composite membrane sample Nos. 106 and 107 were produced in a mannersimilar to the production of the composite membrane No. 101 except thatthe polyacrylonitrile porous membrane was changed to a polysulfoneporous membrane or a polyphenylene oxide porous membrane.

Herein, with regard to the cutoff molecular weight of any of thesepolyacrylonitrile porous membrane, polysulfone porous membrane andpolyphenylene oxide porous membrane, a membrane having 100,000 or lesswas used.

Polymer (P-2) was synthesized using M-5 in place of M-2 in the compositemembrane sample No. 101.

Sample No. 108(P-2), sample No. 109(P-2A), sample No. 110(P-4), sampleNo. 111(P-5) and sample No. 112(P-6) of composite membranes wereproduced in a similar manner except that polymers were changed topolymer (P-2A) in which a functional group density ratio of polymer(P-2) was changed to 0.553, and the weight average molecular weightthereof was changed to 58,000, and also changed to polymers (P-4), (P-5)and (P-6) using commercially available raw materials.

Synthesis of Polymer (P-17)

Into a 1 L three-necked flask, 130 mL of N-methylpyrrolidone and 24.82 g(0.100 mol) of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic anhydride(product number: B1317, manufactured by Tokyo Chemical Industry Co.,Ltd.) were put, and the resultant mixture was stirred under ice-coolingand under a nitrogen flow, and thereto, 81 mL of N-methylpyrrolidonesolution containing 14.78 g (0.090 mol) of 2,3,5,6-tetramethylphenylenediamine (product number: T1457, manufactured by Tokyo ChemicalIndustry Co., Ltd.) and 3.663 g (0.010 mol) of2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (product number: B1415, manufactured by Tokyo Chemical Industry Co., Ltd.) was addeddropwise over 30 minutes while keeping an inside of a system at 10° C.or less. After completion of the dropwise addition, the resultantreaction mixture was stirred at 40° C. for 2.5 hours, and then 150 mL oftoluene was added thereto, and the resultant mixture was further heatedto 180° C., and stirred at the temperature for 6 hours. A toluene-watermixed liquid produced by azeotropy in the middle of the reaction wasdistilled out by a Dean-Stark water separator. After reactioncompletion, the resultant mixture was cooled to vicinity of roomtemperature, and then 400 mL of acetone was added thereto and theresultant mixture was diluted. Into a 5 L stainless steel container,1.15 L of methanol and 230 mL of water were put, the resultant mixturewas stirred, and thereto, the acetone diluted solution of the reactionmixture was added dropwise. A precipitated polymer was subjected tosuction filtration, and air blow drying at 60° C., and thus 38.9 g of apolymer was obtained.

Into a 1 L three-necked flask, 15 g of the polymer obtained and 300 mLof tetrahydrofuran was put, and the resultant mixture was stirred undera nitrogen flow and under room temperature, and completely dissolved.Then, the resultant mixture was stirred under ice-cooling, and thereto,0.45 g (0.005 mol) of acryloyl chloride (product number: A0147,manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise,and 1.05 mL (0.0075 mol) of triethylamine and 0.46 g (0.0038 mol) ofN,N-dimethylaminopyridine (product number: D1450, manufactured by TokyoChemical Industry Co., Ltd.) were further added, and the resultantmixture was stirred under ice-cooling for 1 hour, heated to roomtemperature, and further stirred for 8 hours. Into a 5 L stainless steelcontainer, 1 L of methanol and 200 mL of water were put, the resultantmixture was stirred, and thereto, the reaction mixture was addeddropwise. A precipitated polymer solid was subjected to suctionfiltration, and air blow drying at 40° C., and thus 14.3 g of polymer(P-17) was obtained.

A composite membrane sample No. 113 was produced in a manner similar tothe production of the composite membrane sample No. 101 except that thepolymer (P-17) was used in place of the polymer (P-1), and a solvent wasfurther changed from methyl ethyl ketone to tetrahydrofuran.

Then, (P-22, composite membrane sample No. 114), (P-23, compositemembrane sample No. 115), (P-24, composite-membrane sample No. 116) and(P-29, composite-membrane sample No. 117) were synthesized,respectively, in a manner similar to the production of the compositemembrane sample No. 113 except that polymers were changed in place ofthe polymer (P-17). Further, composite membranes were prepared bycoating them on polyacrylonitrile porous membranes.

[Comparative Samples c11 to c14]Polymer Described in U.S. Pat. No. 7,247,191 B2

Into a 1 L three-necked flask, 100 mL of N-methylpyrrolidone and 12.0 g(0.027 mol) of 6FDA (product number: H0771, manufactured by TokyoChemical Industry Co., Ltd.) were put to allow dissolution at 40° C.,the resultant mixture was stirred under a nitrogen flow, and thereto, 65mL of N-methylpyrrolidone solution containing 3.25 g (0.0216 mol) of2,4-diaminomesitylene (product number: T1275, manufactured by TokyoChemical Industry Co., Ltd.) and 0.82 g (0.0054 mol) of3,5-diaminobenzoic acid (product number: D0294, manufactured by TokyoChemical Industry Co., Ltd.) was added dropwise thereto over 30 minuteswhile keeping an inside of a system at 40° C. The resultant reactionmixture was stirred at 40° C. for 2.5 hours, and then 0.64 g (0.0081mol) of pyridine and 6.89 g (0.068 mol) of acetic anhydride were addedthereto, respectively, and the resultant mixture was stirred at 80° C.for 3 hours. Then, 150 mL of acetone was added to the reaction mixture,and the reaction mixture was diluted. Into a 5 L stainless steelcontainer, 1.5 L of methanol was put and stirred, and thereto, theacetone diluted solution of the reaction mixture was added dropwise. Theobtained polymer crystals were subjected to suction filtration, and airblow drying at 60° C., and thus 8.3 g of polymer (A) was obtained. Tothis polymer (A), ethylene glycol was added in an amount equivalent to3,5-diaminobenzoic acid, the polymer liquid was casted on each poroussupport membrane of polyacrylonitrile, polysulfone and polyphenyleneoxide using an applicator in a manner similar to the operations for thesample No. 101, in a manner similar to the method described in U.S. Pat.No. 7,247,191 B2, and thus crosslinked composite membrane sample Nos.c11, c12 and c13 were produced.

With reference to European Polymer Journal, Vol. 33, No. 10-12,1717-1721 (1997), a photo-curable crosslinkable polyimide-polyphenyleneoxide (PPO) composite membrane sample No. c14 was produced.

Polymer described in European Polymer Journal, 33, 1717 (1997)

(Measurement of Gas Permeability)

With regard to a gas separation composite membrane of each membranesample obtained, a gas permeability measuring device (GTR-10XF,manufactured by GTR Tec Corporation) was used, a mixed gas (1:1) ofcarbon dioxide (CO₂) and methane (CH₄) was used, and each gaspermeability for CO₂ and CH₄ was measured at 40° C. by adjustingpressure on a side of gas supply to 8 atmospheric pressure. The gaspermeability of a membrane was compared by calculating gas transmissionrate as gas permeability (permeance). A unit of the gas permeability(gas transmission rate) was expressed in terms of a GPU unit[1GPU=1×10⁻⁶ cm³ (STP)/cm²·sec·cmHg.].

Moreover, a ratio of transmission rates (TR_(CO2)/TR_(CH4)) from atransmission rate (TR_(CO2)) of carbon dioxide and a transmission rate(TR_(CH4)) of methane as obtained was determined.

(Bending Test [Membrane-Forming Competence Test])

The gas separation composite membrane according to the present inventionis desirably used for a package referred to as a module or an element inwhich the membrane is packed. When the gas separation membrane is usedfor the module, the membranes are packed with high density in order toincrease a membrane surface area, and therefore packed by bending themembranes in a spiral shape in a flat sheet membrane. Therefore,sufficient bending strength should be provided with the membrane. Inorder to confirm the performance, operations of bending each compositemembrane at 180 degrees and unbending the membrane were repeated by 50times, and then whether or not measurement of the gas permeability wasallowed was confirmed.

A: Measurement of permeability was allowed without any problem.

B: Measurement of permeability was not allowed.

The results of the gas permeability and the bending test are shown inTable 2.

TABLE 2 PI molecular Crosslinking Crosslinkable Crosslinking SamplePolymer weight Supporting Crosslinking temperature/ functional groupconversion Crosslinked No. No. (×1000)* membrane form Time density γratio α site ratio η 101 P-1 83 PAN Radical R.T./1 min 0.080 83 0.033102 P-1A 78 PAN Radical R.T./1 min 0.028 70 0.010 103 P-1B 63 PANRadical R.T./1 min 0.006 61 0.002 104 P-1C 60 PAN Radical R.T./1 min0.680 85 0.289 105 P-1 83 PAN Radical R.T./5 sec 0.080 30 0.012 106 P-183 PSf Radical R.T./1 min 0.080 81 0.032 107 P-1 83 PPO Radical R.T./1min 0.080 80 0.032 108 P-2 67 PAN Radical R.T./1 min 0.080 77 0.031 109P-2A 58 PAN Radical R.T./1 min 0.553 79 0.218 110 P-4 80 PAN RadicalR.T./1 min 0.039 77 0.015 111 P-5 94 PAN Radical R.T./1 min 0.050 780.020 112 P-6 67 PAN Radical R.T./1 min 0.080 89 0.036 113 P-17 115 PANRadical R.T./1 min 0.050 94 0.024 114 P-22 138 PAN Radical R.T./1 min0.050 63 0.016 115 P-23 210 PAN Radical R.T./1 min 0.010 67 0.007 116P-24 160 PAN Radical R.T./1 min 0.005 62 0.003 117 P-29 83 PAN RadicalR.T./1 min 0.080 98 0.040 c11 — 105 PAN Ester 150° C., 25 h 0.400 900.180 c12 — 105 PSf Ester 150° C., 25 h 0.400 97 0.192 c13 — 105 PPOEster 150° C., 25 h 0.400 96 0.192 c14 — 83 PPO Radical 80° C., 60 min0.960 96 0.460 150° C., 60 min 165° C., 30 min 190° C., 10 min *Weight-average molecular weight of the polyimide compound before thecrosslinking R.T.: Room temperature Sample No. CO₂ permeability (GPU)CO₂/CH₄ separation selectivity Bending test (Membrane-formingcompetence) 101 94 34 A 102 105 37 A 103 82 25 A 104 38 38 A 105 115 35A 106 80 32 A 107 73 34 A 108 93 33 A 109 38 39 A 110 95 36 A 111 74 32A 112 78 33 A 113 96 35 A 114 78 32 A 115 31 29 A 116 63 29 A 117 70 28A c11 The membrane was broken — B c12 The membrane was broken — B c13 2018 B c14 11 21 B Abbreviations in the above-described Table 2 are asdescribed below. PAN: Polyacrylonitrile PSf: Polysulfone PPO:Polyphenyleneoxide Room temperature: about 25° C. Radical: Radicalcrosslinking Ester: Transesterification

The above-described results show that the gas separation compositemembrane according to the present invention is excellent in both carbondioxide permeability and separation selectivity, and also is providedwith high bending strength.

Example 2

A sample error ratio was evaluated using the gas separation membrane ofeach sample produced in Example 1.

(Sample Error Ratio)

Were produced 50 samples of each of the gas separation membranesdescribed above, permeability of hydrogen of each sample was measured,the sample having a gas permeance higher than 1,000,000 GPU (1×10⁶cm³/cm²·sec·cmHg) was defined as a membrane having pinholes, and a valueobtained by the following equation was calculated as a sample errorratio.

Sample error ratio=(The number of membranes having pinholes/50)×100

The obtained results are shown in Table 3.

TABLE 3 Sample No. Sample error ratio [%] 101 6 102 12 103 18 104 14 1054 106 6 107 6 108 8 109 6 110 10 111 4 112 16 113 12 114 14 115 6 116 4117 8 c11 — c12 — c13 46 c14 66

From the above-described results, the number of pinholes is small forany of the gas separation composite membrane according to the presentinvention. Thus, the results show that a membrane having a good gasseparating layer with few pinholes can be prepared according to thepresent invention.)

The gas separation composite membrane according to the present inventionhas no excessively high crosslinked site ratio, has practical gaspermeability, and is further excellent in mechanical strength. Further,a composite membrane with a porous supporting membrane can be obtainedat a low temperature and in a short time. Therefore, a practical gasseparation composite membrane can be obtained without depending on aglass transition temperature of the porous support.

The above-described results show that the gas separation compositemembrane according to the present invention is excellent in gaspermeability and gas separation selectivity, particularly, permeabilityof carbon dioxide, and excelled as the separation membrane of carbondioxide/methane. Further, the composite membrane can be prepared at alow temperature and in a short time, and therefore is excellent inproduction competence.

As described above, through the gas separation membrane and thecomposite membrane of the present invention, it is possible to provide asuperior gas separation method, a gas separation module, a gasseparation method using the gas separation module, and a gas separationapparatus.

Having described our invention as related to the present embodiments, itis our intention that the invention not be limited by any of the detailsof the description, unless otherwise specified, but rather be construedbroadly within its spirit and scope as set out in the accompanyingclaims.)

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2011-165378 filed in Japan on Jul. 28,2011, which is entirely herein incorporated by reference.

REFERENCE SIGNS LIST

-   1 Gas separating layer-   2 Porous layer-   3 Nonwoven fabric layer-   10 and 20 Gas separation composite membrane

1. A gas separation composite membrane, comprising: a gas-permeablesupporting layer; and a gas separating layer containing a crosslinkedpolyimide resin over the gas-permeable supporting layer, wherein thecrosslinked polyimide resin is formed by a polyimide compound beingcrosslinked by a radically crosslinkable functional group thereof, andwherein a ratio [η] of a crosslinked site to an imide group of thepolyimide compound (the number of crosslinked sites/the number of imidegroups) in the crosslinked polyimide resin is 0.0001 or more and 0.45 orless.
 2. The gas separation composite membrane according to claim 1,wherein a crosslinking conversion ratio [α] of the crosslinked polyimideresin is 20% or more and 100% or less.
 3. The gas separation compositemembrane according to claim 1, wherein the radically crosslinkablefunctional group contains an ethylenically unsaturated group.
 4. Theseparation composite membrane according to claim 1, wherein theradically crosslinkable functional group contains a linking group inwhich a crosslinked structural site is represented by —C(R^(A1))₂CH₂—;and wherein R^(A1) represents a hydrogen atom, an alkyl group having 1to 10 carbon atoms, —R^(A2)—C(═O)O— or —R^(A2)—OC(═O)—, and R^(A2)represents an alkylene having 1 to 10 carbon atoms.
 5. The gasseparation composite membrane according to claim 1, wherein thepolyimide compound contains a repeating unit represented by Formula (I):

wherein R represents a structure part containing at least onehydrocarbon ring having 5 to 12 carbon atoms.
 6. The separationcomposite membrane according to claim 5, wherein the polyimide compoundfurther contains at least one kind of repeating unit represented byFormula (II-a) or (II-b), and at least one kind of repeating unitrepresented by Formula (III-a) or (III-b), and wherein R of therepeating unit represented by Formula (I) is a group of atoms selectedfrom the group consisting of the groups represented by any one ofFormulas (I-a) to (I-g):

wherein, in Formulas (I-a) to (I-g), X¹ represents a single bond or abivalent linking group; Y¹ represents a methylene group or a vinylenegroup; R¹ and R² each independently represent a hydrogen atom or asubstituent, or may bond with each other to form a ring; and the symbol“*” represents a binding site with the carbonyl group of the imide inFormula (I);

wherein, in Formulas (II-a) and (II-b), R³ represents an alkyl group, ahydroxyl group, a carboxyl group, a sulfonic acid group, an amino groupor a halogen atom; l1 represents an integer of from 0 to 4; R⁴ and R⁵each independently represent an alkyl group, a hydroxyl group, acarboxyl group, a sulfonic acid group, an amino group or a halogen atom;R⁴ and R⁵ may bond with each other to form a ring; m1 and n1 eachindependently represent an integer of from 0 to 4; and X² represents asingle bond or a bivalent linking group; and

wherein, in Formulas (III-a) and (III-b), R⁶, R⁷ and R⁸ eachindependently represent a substituent; R⁷ and R⁸ may bond with eachother to form a ring; J^(r), J² and W¹ each independently represent asingle bond or a bivalent linking group; l2, m2 and n2 eachindependently represent an integer of from 0 to 3; L¹ represents abivalent linking group; L² represents a functional group; p representsan integer of 0 or more; when p is 2 or more, L¹'s and J²'s may be thesame or different from each other; and X³ represents a single bond or abivalent linking group.
 7. The separation composite membrane accordingto claim 6, wherein X¹ is a single bond, —C(Ra)₂-, —O—, —SO₂—, —C(═O)—,or —S—; and Ra is a hydrogen atom or an alkyl group.
 8. The gasseparation composite membrane according to claim 6, wherein R¹ and R²each independently represent a hydrogen atom, an alkyl group, acycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, anamino group, an alkoxy group, an aryloxy group, a heterocyclic oxygroup, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group,an acyloxy group, an acylamino group, an alkoxycarbonylamino group, anaryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, acarbamoyl group, an alkylthio group, an arylthio group, a heterocyclicthio group, a sulfonyl group, a sulfinyl group, a ureido group, aphosphoric acid amide group, a hydroxyl group, a mercapto group, ahalogen atom, a cyano group, a sulfo group, a carboxyl group, an oxogroup, a nitro group, a hydroxamic acid group, a sulfino group, ahydrazino group, an imino group, a heterocyclic group, a silyl group, ora silyloxy group.
 9. The separation composite membrane according toclaim 6, wherein X² is a single bond, —C(Ra)₂-, —O—, —SO₂—, —C(═O)—, or—S—; and Ra is a hydrogen atom or an alkyl group.
 10. The separationcomposite membrane according to claim 6, wherein R⁶, R⁷ and R⁸ inFormulas (III-a) and (III-b) each independently represent an alkylgroup, a cycloalkyl group, an alkenyl group, an alkynyl group, an arylgroup, an amino group, an alkoxy group, an aryloxy group, a heterocyclicoxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonylgroup, an acyloxy group, an acylamino group, an alkoxycarbonylaminogroup, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoylgroup, a carbamoyl group, an alkylthio group, an arylthio group, aheterocyclic thio group, a sulfonyl group, a sulfinyl group, a ureidogroup, a phosphoric acid amide group, a hydroxyl group, a mercaptogroup, a halogen atom, a cyano group, a sulfo group, a carboxyl group,an oxo group, a nitro group, a hydroxamic acid group, a sulfino group, ahydrazino group, an imino group, a heterocyclic group, a silyl group, ora silyloxy group.
 11. The separation composite membrane according toclaim 6, wherein J¹ and J² in Formulas (III-a) and (III-b) eachindependently represent a single bond, *—O—**, *—S—**, *—C(═O)—**,*—C(═O)O—**,*—C(═O)NR⁹—**, *—OC(═O)—**, *—COO⁻NH⁺(R¹⁰)(R¹¹)—**, *—SO₃⁻NH⁺(R¹²)(R¹³)—**, a methylene group, a phenylene group, or*—C₆H₅C(═O)—**; and the symbol “*” represents a bonding hand on a sideof L¹ for J² or on a side of the phenylene group for J¹, and the symbol“**” represents a bonding hand reverse thereto.
 12. The separationcomposite membrane according to claim 6, wherein W¹ in Formulas (III-a)and (III-b) represents a single bond, an alkylene group, an alkyleneoxygroup, an aralkylene group, or an arylene group.
 13. The separationcomposite membrane according to claim 6, wherein L¹ in Formulas (III-a)and (III-b) is any one of formulas (L-1) to (L-35) described below, analkylene group, an alkyleneoxy group or an arylene group.


14. The separation composite membrane according to claim 6, wherein L²in Formulas (III-a) and (III-b) is a (meth)acryloyl group, a(meth)acryloyloxy group, a (meth)acryloylamino group, a vinyl group, anallyl group or a styryl group.
 15. The separation composite membraneaccording to claim 6, wherein X³ is a single bond, —C(Ra)₂-, —O—, —SO₂—,—C(═O)—, or —S—; and Ra is a hydrogen atom or an alkyl group.
 16. Thegas separation composite membrane according to claim 6, wherein therepeating unit represented by Formula (III-a) is represented by Formula(III-a1):

wherein R⁶, l², J¹, W¹, L¹, J², L² and p have the same meaning as thosein Formula (III-a), respectively.
 17. The separation composite membraneaccording to claim 6, wherein a ratio of the functional group L² of therepeating unit represented by Formula (III-a) or (III-b) to therepeating unit represented by Formula (I) (the number of functionalgroup L²'s/the number of repeating units represented by Formula (I)) isfrom 0.003 to 0.68.
 18. The separation composite membrane according toclaim 1, wherein the supporting layer contains a porous layer on a sideof the gas separating layer and a nonwoven fabric layer on a sidereverse thereto.
 19. The separation composite membrane according toclaim 18, wherein the porous layer has a molecular weight cut-off of100,000 or less.
 20. The separation composite membrane according toclaim 1, wherein a gas to be supplied is a mixed gas of carbon dioxideand methane, wherein a transmission rate of the carbon dioxide at 40° C.and 8 atmospheric pressure is more than 20 GPU, and wherein a ratio ofthe transmission rate of the carbon dioxide to a transmission rate ofthe methane (TR_(CO2)/TR_(CH4)) is 20 or more.
 21. A method of producinga gas separation composite membrane, wherein the gas separationcomposite membrane contains a gas-permeable supporting layer, and a gasseparating layer containing a crosslinked polyimide resin over thegas-permeable supporting layer, wherein the method comprises the stepsof: coating a coating liquid containing a polyimide compound having aradically crosslinkable functional group over the supporting layer, andallowing reaction of the crosslinkable functional group by irradiatingthe coating liquid with active radiation or providing the coating liquidwith heat to crosslink the polyimide compound, and wherein a ratio [η]of a crosslinked site to an imide group of the polyimide compound (thenumber of crosslinked sites/the number of imide groups) is adjusted tobe 0.0001 or more and 0.45 or less.
 22. The method of producing a gasseparation composite membrane, wherein the gas separation compositemembrane contains a gas-permeable supporting layer, and a gas separatinglayer containing a crosslinked polyimide resin over the gas-permeablesupporting layer, wherein the method comprises the steps of: coating acoating liquid containing a polyimide compound having a radicallycrosslinkable functional group over the supporting layer, and allowingreaction of the crosslinkable functional group by irradiating thecoating liquid with active radiation or providing the coating liquidwith heat to crosslink the polyimide compound, and wherein acrosslinking conversion ratio [α] is adjusted to be 20% or more and 100%or less.
 23. A gas separation module, comprising the gas separationcomposite membrane according to claim
 1. 24. A gas separation apparatus,comprising the gas separation module according to claim
 23. 25. A gasseparation method, which comprises a step of selectively permeatingcarbon dioxide from a gas containing carbon dioxide and methane by usingthe gas separation composite membrane according to claim 1.